Unable to create specialized list tab off one custom entity to another

I have a two custom entities: one is a primary called 'Job' , the other is a secondary called Bid2WinUserFields. Both entities store their parent Opportunity ID. We have a .Net DLL tab that displays the Bid2WinUserFields as a list tab off the Opportunity. This works just fine. The client wants to display the same tab off the Opportunity - so I need to somehow set the FilterByContextID to the Opportunity ID from withint the Job context. I am retrieving the Opp ID correctly as indicated by my log entry:

Jul 31 2013 15:09:30.453 18140 17208 5 OppID = 836

However the code below produces the .Net log error at the bottom:

Build error: WebObject Get Key Error:GetKey exception, key is out of bounds: 836

So is this even possible? If so, what am I doing wrong? Any help is greatly appreciated. Thanks.

CODE:

using System;
using System.Collections.Generic;
using System.Text;
using Sage.CRM.WebObject;

namespace Job_B2WUserDefinedFields.DataPages
{
public class B2WUserFieldsListPage : ListPage
{
public B2WUserFieldsListPage()
: base("B2WUserFields", "B2W_UserFieldsList", "B2W_UserFieldsFilter")
{

int OppID = int.Parse(GetContextInfo("job", "job__opportunityid"));
LogMessage("_JobB2W", "OppID = " + OppID.ToString(), 5);
FilterByField = "b2wuf_opportunityid";
FilterByContextId = OppID;
}

public
override void BuildContents()
{
try
{
base.BuildContents();
}
catch (Exception error)
{
this.AddError(error.Message);
}
}
}
}

.NET LOG

Jul 31 2013 15:09:30.313 18140 17208 5 Set WebPage object reference.
Jul 31 2013 15:09:30.329 18140 17208 5 Loading CRM Interfaces:
Jul 31 2013 15:09:30.329 18140 17208 5 LOADING MAIN INTERFACES
Jul 31 2013 15:09:30.438 18140 17208 5 Got assembly: Job_B2WUserDefinedFields, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
Jul 31 2013 15:09:30.438 18140 17208 5 EntryPoint - Initializing dotnet objects
Jul 31 2013 15:09:30.438 18140 17208 5 Type: Job_B2WUserDefinedFields.DataPages.B2WUserFieldsDataPageNew, BaseClass: Sage.CRM.WebObject.DataPageNew
Jul 31 2013 15:09:30.438 18140 17208 5 Is Class: True; Is AppFactory: False
Jul 31 2013 15:09:30.438 18140 17208 5 Type: Job_B2WUserDefinedFields.DataPages.B2WUserFieldsSearchPage, BaseClass: Sage.CRM.WebObject.SearchPage
Jul 31 2013 15:09:30.438 18140 17208 5 Is Class: True; Is AppFactory: False
Jul 31 2013 15:09:30.438 18140 17208 5 Type: Job_B2WUserDefinedFields.DataPages.B2WUserFieldsListPage, BaseClass: Sage.CRM.WebObject.ListPage
Jul 31 2013 15:09:30.438 18140 17208 5 Is Class: True; Is AppFactory: False
Jul 31 2013 15:09:30.438 18140 17208 5 Type: Job_B2WUserDefinedFields.DataPages.B2WUserFieldsDataPageDelete, BaseClass: Sage.CRM.WebObject.DataPageDelete
Jul 31 2013 15:09:30.438 18140 17208 5 Is Class: True; Is AppFactory: False
Jul 31 2013 15:09:30.438 18140 17208 5 Type: Job_B2WUserDefinedFields.DataPages.B2WUserFieldsDataPage, BaseClass: Sage.CRM.WebObject.DataPage
Jul 31 2013 15:09:30.438 18140 17208 5 Is Class: True; Is AppFactory: False
Jul 31 2013 15:09:30.438 18140 17208 5 Type: Job_B2WUserDefinedFields.AppFactory, BaseClass: System.Object
Jul 31 2013 15:09:30.438 18140 17208 5 Is Class: True; Is AppFactory: True
Jul 31 2013 15:09:30.438 18140 17208 5 AppFactory found
Jul 31 2013 15:09:30.438 18140 17208 5 Invoking Method: RunListPage; DLL: Job_B2WUserDefinedFields, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
Jul 31 2013 15:09:30.453 18140 17208 5 Casting the Method result to Sage.CRM.WebObject.Web
Jul 31 2013 15:09:30.453 18140 17208 5 Before invoke BuildContents
Jul 31 2013 15:09:30.485 18140 17208 5 WebObject Get Key Error:GetKey exception, key is out of bounds: 836
Jul 31 2013 15:09:30.485 18140 17208 1 Class: ListPage - Method: BuildContents - Error: Error HRESULT E_FAIL has been returned from a call to a COM component.
Jul 31 2013 15:09:30.500 18140 17208 5 Unloading Domain
Jul 31 2013 15:09:30.500 18140 17208 5 NET - BASE RELEASE CORE INTERFACES
Jul 31 2013 15:09:30.500 18140 17208 5 Metadata Unload.
Jul 31 2013 15:09:30.500 18140 17208 5 Keys Unload.
Jul 31 2013 15:09:30.500 18140 17208 5 UserSession Unload.
Jul 31 2013 15:09:30.500 18140 17208 5 Dispatch Unload.
Jul 31 2013 15:09:30.500 18140 17208 5 Unloading WebPage