Hey there, 

I am new to salesforce dev and am having issues getting a visual force page to open from a custom list button on a custom object. When I click the custom list button from the object (sales activity) , my page doesnt open and a standard add contact form does. I've researched a bit in this forum, and learned that this can be due to a missing standard controller. I followed that advice and dont think that is my issue, although I could very easily be wrong. The full page source is below, meant to allow users to add a contact from various sources to be an 'Impact Contact'. What I think might be the issue is in the custom controller, which I also have the code listed below. 

<apex:page standardController="IMPACT_Contact__c" recordSetVar="contacts" extensions="IMPACTContactExt" title="Add IMPACT Contacts to Sales Activity">


    <apex:tabPanel switchType="client" selectedTab="available" id="contactPanel">
        <apex:tab label="Available Contacts" name="available" id="tabAvailable">
            <apex:form id="formAddContact">
            <apex:pageBlock title="Available Contacts">
                <apex:pageBlockButtons >
                    <apex:commandButton action="{!addOthers}" value="Add Selected Contacts" reRender="otherContacts, existingContactsTable"/>
                    <apex:commandButton action="{!done}" value="Done"/>
                </apex:pageBlockButtons>
                 <apex:selectCheckboxes id="otherContacts" layout="pageDirection" value="{!otherSelectedContacts}">
                    <apex:selectOptions value="{!otherContacts}"/>
                </apex:selectCheckboxes>
            </apex:pageBlock>
            </apex:form>        
        </apex:tab>

        <apex:tab label="Find Contacts" name="find" id="tabFind">
            <apex:form id="formFindContact">
                <apex:pageBlock title="Find Contacts">
                    <apex:pageBlockButtons >
                        <apex:commandButton action="{!findContacts}" value="Find Contacts" reRender="findResults"/>
                        <apex:commandButton action="{!addFound}" value="Add Selected Contacts" reRender="findResults, existingContactsTable"/>
                        <apex:commandButton action="{!done}" value="Done" immediate="true" />
                    </apex:pageBlockButtons>
                    <apex:outputPanel id="findResults">
                        <apex:pageBlockSection title="Contact to Find" columns="1">
                            <apex:inputField value="{!findContact.FirstName}" />
                            <apex:inputField value="{!findContact.LastName}" required="true" />
                        </apex:pageBlockSection>
                        <apex:selectCheckboxes id="foundContacts" layout="pageDirection" value="{!foundSelectedContacts}">
                            <apex:selectOptions value="{!foundContacts}"/>
                        </apex:selectCheckboxes>
                        <apex:outputPanel id="noContactsFound"  rendered="{! IF(AND(foundContacts.size = 0, findContact.LastName <> null), 'TRUE', 'FALSE') }">
                            There were no contacts found matching your search criteria.
                        </apex:outputPanel>
                    </apex:outputPanel>
    
                </apex:pageBlock>
            </apex:form>        
        </apex:tab>

        <apex:tab label="Create New Contact" name="new" id="tabNew">
            <div>
                Use this form to add a new contact to Salesforce and associate it 
                with this sales activity with the selected role.  A search of existing contacts will
                be conducted automatically before the new contact record is created. If
                an existing contact is found, they will be associated with the sales activity.
            </div>
            <apex:form id="formNewContact">
                <apex:pageBlock >
                    <apex:pageBlockButtons >
                        <apex:commandButton action="{!addNew}" value="Save and Add" reRender="newContactSection, existingContactsTable"/>
                        <apex:commandButton action="{!done}" value="Done" immediate="true" />
                    </apex:pageBlockButtons>
                    <apex:pageBlockSection columns="2" id="newContactSection">
                        <apex:inputField value="{!newContact.FirstName}" required="true"/>
                        <apex:inputField value="{!newContact.LastName}" required="true"/>
                        <apex:inputField value="{!newContact.Title}"/>
                        <apex:inputField value="{!newContact.Phone}"/>
                        <apex:inputField value="{!newContact.Email}"/>
                        <apex:inputField value="{!newContact.AccountID}" required="true"/>
                        <apex:inputField value="{!newIMPACTContact.Contact_Role__c}" required="true"/>
                        {!addContactResult}
                    </apex:pageBlockSection>
                </apex:pageBlock>
            </apex:form>
        </apex:tab>        

        <apex:tab label="Existing Key Contacts" name="existing" id="tabExisting">
            <apex:form id="formExistingContact">
                <apex:pageBlock title="Associated Contacts">
                    <apex:pageBlockButtons >
                        <apex:commandButton action="{!done}" value="Done"/>
                    </apex:pageBlockButtons>            
                    <apex:pageBlockTable value="{!impactContacts}" var="ic" id="existingContactsTable">
                        <apex:column value="{!ic.Contact__r.Name}"/>
                        <apex:column value="{!ic.Contact__r.Title}"/>
                        <apex:column value="{!ic.Contact__r.Account.Name}"/>
                        <apex:column value="{!ic.Contact_Role__c}"/>
                    </apex:pageBlockTable>
                </apex:pageBlock>
            </apex:form>
        </apex:tab>
        
        
    </apex:tabPanel>

When attempting to preview my page, I get an error <List has no rows for assignment to SObject > which makes me think I have an issue with my query, specifically

this.salesActivity

So My questions are this: Will a query mistake in the custom controller prevent the entire page from loading, including all tabs, formatting, etc? and secondly, is there anything glaringly obvious with the way I am approaching this that is wrong? I have been researching the issue and am pretty stuck now. 

public with sharing class IMPACTContactExt {
    private final IMPACT_Contact__c  impactContact;
    private final Sales_Activity__c  salesActivity;
    
    public IMPACTContactExt(ApexPages.StandardSetController controller) {
        
        this.impactContact = (IMPACT_Contact__c)controller.getRecord();
        this.salesActivity = [SELECT Id, Activity_Type__c, Activity_Status__c FROM Sales_Activity__c WHERE Id = :ApexPages.currentPage().getParameters().get('id')];
    
    }
    
    public IMPACTContactExt(Sales_Activity__c p) {
        this.salesActivity = [SELECT Id, Activity_Type__c, Activity_Status__c FROM Sales_Activity__c WHERE Id = :p.Id];
    }
    
    public IMPACT_Contact__c newIMPACTContact {
        get{ 
            if (newIMPACTContact == null) newIMPACTContact = new IMPACT_Contact__c(Sales_Activity__c = salesActivity.Id);
            return newIMPACTContact; 
        } 
        set;
    }
    
    public Contact newContact {
        get{ 
            if (newContact == null ) newContact = new Contact();
            return newContact; 
        } 
        set;
    }
    
    public String addContactResult {get; set;}
    
    public Contact findContact {
        get{ 
            if (findContact == null ) findContact = new Contact();
            return findContact; 
        } 
        set;
    }

    public List<IMPACT_Contact__c> getIMPACTContacts() {
        List<IMPACT_Contact__c> impactContacts;
    
        if(impactContacts == null){
            impactContacts = [
                SELECT 
                    Name
                    ,Id
                    ,Contact__r.Title
                    ,Contact__r.Email
                    ,Contact__r.Phone
                    ,Contact__r.Name
                    ,Contact__r.AccountId
                    ,Contact__r.Account.Name
                    ,Contact__r.Id
                    ,Contact__c
                    ,Contact_Role__c 
                FROM IMPACT_Contact__c
                WHERE Sales_Activity__c = :salesActivity.Id
            ];
        }
        
        return impactContacts;
    }

    private Set<ID> GetExistingContactIds() {
        Set<ID> existingContacts = new Set<ID>();
            
        for (IMPACT_Contact__c c : [SELECT Contact__r.Id FROM IMPACT_Contact__c WHERE Sales_Activity__c = :salesActivity.Id ])
            existingContacts.add(c.Contact__r.Id);
        
        return existingContacts;
    }
    
    
    public String[] otherSelectedContacts {
        get{
            if (otherSelectedContacts == null) otherSelectedContacts = new String[]{};
            return otherSelectedContacts;
        }
        set;
    }
    
    public String[] foundSelectedContacts {
        get{
            if (foundSelectedContacts == null) foundSelectedContacts = new String[]{};
            return foundSelectedContacts;
        }
        set;
    }
    
    public List<Selectoption> otherContacts {
        get {
            List<Contact> otherContacts;
            List<Selectoption> otherContactSelect = new List<Selectoption>();
            List<ID> accounts = new List<ID>();
            Set<ID> existingContacts = GetExistingContactIds();
            
            if (salesActivity.Activity_Type__c != null) accounts.add(salesActivity.Activity_Type__c);
            if (salesActivity.Activity_Status__c != null) accounts.add(salesActivity.Activity_Status__c);
    
            otherContacts = [
                SELECT Id, Title, Name, Account.Name
                FROM Contact
                WHERE AccountId IN :accounts AND Id NOT IN :existingContacts
            ];
            
            for (Contact c : otherContacts) {
                String contactDescription = c.Name;
                if (c.Title != null && c.Account.Name != null) {
                    contactDescription += ', ' + c.Title + ' - ' + c.Account.Name;
                } else if (c.Title != null) {
                    contactDescription += ', ' + c.Title;
                    
                } else if (c.Account.Name != null) {
                    contactDescription += ' - ' + c.Account.Name;
                }

                otherContactSelect.add(new Selectoption(c.Id, contactDescription));
            }
            
            return otherContactSelect;
        }
        set;
    }
    
    public List<Selectoption> foundContacts {
        get {
            if(foundContacts == null) foundContacts = new List<Selectoption>();
            return foundContacts;
        }
        set;
    }
    
    public PageReference findContacts() {

        if (findContact.LastName != null) {
            String newContactName;
            if(findContact.FirstName != null) {
                newContactName = findContact.FirstName + ' ' + findContact.LastName;
            } else {
                newContactName = findContact.LastName;
            }
            
            List<List<Sobject>> contactSearch = [FIND :newContactName IN NAME FIELDS RETURNING Contact(Id, Name, Title, Account.Name)];
            Contact [] contactsFound = ((List<Contact>)contactSearch[0]);
            foundContacts = new List<Selectoption>();
    
            if (contactsFound.size() != 0) {
                Set<ID> existingContacts = GetExistingContactIds();
                
                for(Contact c : contactsFound) {
                    // don't add a contact if it is already on our list
                    if (existingContacts.contains(c.Id)) continue;
                        
                    String contactDescription = c.Name;
                    if (c.Title != null && c.Account.Name != null) {
                        contactDescription += ', ' + c.Title + ' - ' + c.Account.Name;
                    } else if (c.Title != null) {
                        contactDescription += ', ' + c.Title;
                        
                    } else if (c.Account.Name != null) {
                        contactDescription += ' - ' + c.Account.Name;
                    }
                    
                    foundContacts.add(new Selectoption(c.Id, contactDescription));
                }
            }
        } else {
            foundContacts = new List<Selectoption>();
        }
        
        return null;
    }   
    
    public PageReference addNew() {
        // search for the contact before adding
        String findContactName;
        
        if (newContact.FirstName == null) {
            findContactName =  newContact.LastName;
        } else {
            findContactName =  newContact.FirstName + ' ' + newContact.LastName;
        }
        
        Boolean matchFound = false; 
        List<List<Sobject>> contactSearch = [FIND :findContactName IN NAME FIELDS RETURNING Contact(Id, FirstName, LastName, Phone, Email, AccountId)];
        Contact [] contactsFound = ((List<Contact>)contactSearch[0]);
        
        if (contactsFound.size() != 0) {
            for(Contact c : contactsFound) {
                if (newContact.LastName == c.LastName && (newContact.Phone == c.Phone || newContact.Email == c.Email)) {
                    newContact = c;
                    addContactResult = 'An existing contact was found that matched your input.  This contact was added to the Sales Activity and can be seen by going to the Existing IMPACT Contacts tab.';
                    matchFound = true; 
                    break;
                }
            }
        }
        
        if (matchFound == false) {
            insert newContact;
            addContactResult = 'New contact created and added to the sales activity.  You can view this contact by going to the Existing IMPACT Contacts tab.';
        }
        
        newIMPACTContact.Contact__c = newContact.Id;
        insert newIMPACTContact;
        
        newContact = null;
        newIMPACTContact = null;
        
        return null;
    }
    
    public PageReference addOthers() {
        List<IMPACT_Contact__c> impactContacts = new List<IMPACT_Contact__c>();
        
        for (String opt : otherSelectedContacts) {
            impactContacts.add(new IMPACT_Contact__c(Contact__c = opt, Sales_Activity__c = salesActivity.Id));
        }
        
        insert impactContacts;
        
        return null;
    }
    
    public PageReference addFound() {
        List<IMPACT_Contact__c> impactContacts = new List<IMPACT_Contact__c>();
        List<Integer> optionsToRemove = new List<Integer>();
        
        for (String opt : foundSelectedContacts) {
            impactContacts.add(new IMPACT_Contact__c(Contact__c = opt, Sales_Activity__c = salesActivity.Id));
        }

        insert impactContacts;
        
        // go through the found contacts list and remove any contacts we just added
        // to the sales Activity
        for (Integer i = 0; i <= foundContacts.size() - 1; i++) {
            for (String opt : foundSelectedContacts) {
                if (opt == foundContacts[i].getValue()) {
                    optionsToRemove.add(i);
                    break;
                }
            }
        }

        for (Integer i : optionsToRemove) {
            foundContacts.remove(i);
        }

        return null;
    }
    
    public PageReference done() {
        PageReference salesActivityPage = new ApexPages.StandardController(salesActivity).view();
        salesActivityPage.setRedirect(true);
        
        return salesActivityPage;
    }



}