HI,
 Ive been trying to take example code from a post and work with it in my org, I've done all the step correctly I believe?  but I am getting an error: The Id in the error is belongs to the opportunity record. It happens when i click my custom button. 

If there is another way to recreate a configuration I would be interested in getting that information as well. 

Visualforce Error 
Id value 00618000007xXxxX is not valid for the QuoteRequest__c standard controller

The link to the post :
https://www.verticalcoder.com/2012/05/04/a-poor-mans-product-configurator/

my custom obejct Yushin_Product__c takes the place of the CustomProduct__c object in the example 

My Code:

<apex:page standardController="QuoteRequest__c" extensions="BL_QuoteRequestExtension">
  <apex:form >
    <apex:pageBlock >
      <apex:pageMessages />
      <apex:pageBlockButtons >
        <apex:commandButton value="Save" action="{!save}"/>
        <apex:commandButton value="Cancel" action="{!Cancel}"/>
      </apex:pageBlockButtons>
      <apex:pageBlockSection title="Custom Product" collapsible="false">
        <apex:outputField value="{!QuoteRequest__c.Yushin_Product__c}"/>
      </apex:pageBlockSection>
      <apex:pageBlockSection columns="1" title="Options" collapsible="false">
        <apex:repeat value="{!$ObjectType.QuoteRequest__c.FieldSets.Group1}" var="f" >
          <apex:inputfield value="{!QuoteRequest__c[f]}" rendered="{!CustomProduct.Equipment_Type__c == 'Group1'}"/>
        </apex:repeat>
        <apex:repeat value="{!$ObjectType.QuoteRequest__c.FieldSets.Group2}" var="f" >
          <apex:inputfield value="{!QuoteRequest__c[f]}" rendered="{!CustomProduct.Equipment_Type__c == 'Group2'}"/>
        </apex:repeat>
      </apex:pageBlockSection>
    </apex:pageBlock>
  </apex:form>
</apex:page>

 

public with sharing class BL_QuoteRequestExtension {
    
  public Yushin_Product__c CustomProduct {get; set;}
  private final QuoteRequest__c opps;
 
  public BL_QuoteRequestExtension(ApexPages.StandardController controller) {
    this.opps = (QuoteRequest__c)controller.getRecord();
    try {
      CustomProduct = [select id, Equipment_Type__c from Yushin_Product__c where id=
                       :ApexPages.currentPage().getParameters().get('Yushin_Product__c')];
    } catch(Exception e) {
      ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.FATAL, 'Error Getting Product Info'));
    }
    if (CustomProduct != null)
    
      this.opps.Yushin_Product__c = CustomProduct.Id;
  }
}