I wasn't sure where to post this given the amount of info involved.  I have created a custom "log a call" page using a vf page attached to a button in the account layout.  I have this setup and running correctly in my sandbox environment when I am logged in (system admin).  When I login as anothe user it works correctly as well, but when I have a user login directly to the sandbox to test it generated the following exception...

Force.com Sandbox

Apex script unhandled exception by user/organization: 00540000000oRuq/00DQ0000000Db4h Source organization: 00D40000000Iqhe (null) Visualforce Page: /apex/Log_A_Call_in_Chatter

caused by: System.QueryException: List has no rows for assignment to SObject

Class.LogACallControllerExtension.getAccount: line 8, column 17 External entry point

Since this acutally posts items in Chatter, I don't want to move it over to production yet since I don't want any bogus information in our production org from testing to make sure it is working.  The vf page, controller and button URL are as follows...

<apex:page standardController="Task" extensions="LogACallControllerExtension" showHeader="false" sidebar="false">
<script>
  function refresh(){
   window.close();
   }
</script>
    <apex:sectionHeader title="Log A Call for..."/>
    <apex:form id="pageForm">
        <apex:pageBlock title="{!account.name}" mode="edit">
            <apex:pageBlockButtons location="bottom">
                <apex:commandButton value="Save" action="{!save}" onclick="refresh()" />
                <!--<apex:actionSupport event="onclick" action="{!CreatePost}" /> -->
                <apex:commandButton value="Cancel" action="{!cancel}" onclick="refresh()"/>
            </apex:pageBlockButtons>
            <br />
            <apex:pageBlockSection title="Call Information">
                <apex:inputField value="{!Task.Description}" style="width:400px;height:100px;" />
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>

public with sharing class LogACallControllerExtension {

    public Task task {get; set;}
    public String CallInfo {get; set;}
    ApexPages.StandardController controller;
    
    public Account getAccount() {
         return [SELECT Id, name from Account
             WHERE Id=:ApexPages.currentPage().getParameters().get('what_id')];
    }

    public LogACallControllerExtension(ApexPages.StandardController controller) {
            task = (Task)controller.getRecord();
            task.whatId = ApexPages.currentPage().getParameters().get('what_id');    
            task.subject = 'Service Call';
            task.type = 'Call';
            task.status = 'Completed';
            task.activitydate = Date.today();
//            task.description = CallInfo;
    }
    public PageReference Save()
    {
        FeedItem cpost = new FeedItem();
        cpost.ParentId = ApexPages.currentPage().getParameters().get('what_id');
        cpost.Body = task.description;
        try{
          insert(task);
          insert cpost;
          }
        catch(System.DMLException e){
          ApexPages.addMessages(e);
          return null;
          }
          return(new ApexPages.StandardController(task)).view();
    }
}

/apex/Log_A_Call_in_Chatter?title=Call&what_id={!Account.Id}&followup=1&tsk5=Service Call&retURL=%2F{!Account.Id}&tsk3={!Account.Name}&tsk10=Call

 I am guessing there are some rights involved, but I wasn't aware that the system sees us differently when logged in as someone compared to that person logged in themselves.  Any suggestions on improvement to the code is welcomed as well.