Unexpected Exceptions in SQL/COM+ Since Converting to VS 2005

We are running a COM+ DLL that handles transactions and security with a SQL Server back-end. This project was started in VS 2003, but we just converted it to VS 2005. Since the conversion, creating a number of transactions in a row generates errors at consistent, but moving, locations in the code (i.e. the location where the failure occurs changes when I do things such as add additional try/catch statements, so it is not random but also clearly not associated with any particular line of code).

In the application, the error appears as follows:
-------
System.InvalidCastException was unhandled
Message="Unable to cast COM object of type 'System.__ComObject' to interface type 'System.IDisposable'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{805D7A98-D4AF-3F0F-967F-E5CF45312D2C}' failed due to the following error: COM+ activation failed because the activation could not be completed in the specified amount of time. (Exception from HRESULT: 0x8004E024)."
Source="mscorlib"
StackTrace:
    Server stack trace:
       at System.IDisposable.Dispose()
       at System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr md, Object[] args, Object server, Int32 methodPtr, Boolean fExecuteInContext, Object[]& outArgs)
       at System.Runtime.Remoting.Messaging.StackBuilderSink.PrivateProcessMessage(RuntimeMethodHandle md, Object[] args, Object server, Int32 methodPtr, Boolean fExecuteInContext, Object[]& outArgs)
       at System.Runtime.Remoting.Messaging.StackBuilderSink.SyncProcessMessage(IMessage msg, Int32 methodPtr, Boolean fExecuteInContext)
    Exception rethrown at [0]:
       at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
       at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
       at System.IDisposable.Dispose()
       at MyDataTest.FormMain.GenerateLargeAssociation() in C:\Katana\Projects\Reserves Plus ASP\Testing\RPlusDataTest\FormMain.cs:line 560
       at RPlusDataTest.FormMain.btnEvil_Click_1(Object sender, EventArgs e) in C:\Katana\Projects\Reserves Plus ASP\Testing\RPlusDataTest\FormMain.cs:line 467
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at RPlusDataTest.FormMain.Main() in C:\Katana\Projects\Reserves Plus ASP\Testing\RPlusDataTest\FormMain.cs:line 579
       at System.AppDomain.nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
--------

This code worked fine before converting to VS 2005, so the error appears to be part of .NET Framework 2.0. I have changed the following timeouts to no avail:
-- SQL Connection Timeout (in connection string)
-- SQL Lifetime Timeout (in connection string)
-- Transaction Timeout for COM+ (Component Services, My Computer, Properties)
-- Transaction Timeout for the individual COM+ component, as specified in the [Transaction(...)] attribute in C#.
-- Creation Timeout for the individual COM+ component, as specified in the [ObjectPooling(...)] attribute in C#.

Here's the SQL Connection string we're using:
Integrated Security=SSPI;Persist Security Info=False;Initial Catalog=MyDB;Data Source=.;Connection Timeout=30;Connection Lifetime=60;Pooling=True
(Both timeouts were recently doubled, but made no visible difference.)

I have carefully verified that all COM+ objects being created are also being disposed of. In fact, all COM+ object creations are in "using(...)" statements so the disposal will be carried out automatically by C#.

Just to be sure this point is clear: I can use my COM+ object to save about 10 times, and then I get this error. The exact number of times involved varies. (10 seemed like a convenient number, since it is also the maximum pool size, but changing that value did not alter anything.)

I also am getting event-log listings like the following. They seem to be occuring at the same time as the other error:
---------
A condition has occurred that indicates this COM+ application is in an unstable state or is not functioning correctly. Assertion Failure: m_pTxResPool == NULL

Server Application ID: {BEA5C2EB-FCE6-4714-9C83-7D7D1E5DDA2D}

Server Application Instance ID:

{837A856B-3C40-45A9-BE2A-63B8A4B5BE71}

Server Application Name: RPlusData

The serious nature of this error has caused the process to terminate.

COM+ Services Internals Information:

File: d:\qxp_slp\com\com1x\src\comsvcs\txprop\txstream.cpp, Line: 608

Comsvcs.dll file version: ENU 2001.12.4414.308 shp

----------

Other notes: COM+ Server activiation, with object pooling and JITA, Transaction support for this object is required but we get the error on reads (no transaction) as well.

Update: This has now been turned over to Microsoft as a Technical Support Incident. At present, no fix is available but they are reviewing information gathered from our systems.

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