Win03 R2 vs Win2K Adv Svr

Here's the scenario...

Our site:
SQL Server 2000 on a Windows 2000 Advanced Server.
Our client application on a mix of Windows XP Pro PC's.
Application can access database on SQL just fine.

Client site:
SQL Server 2000 on a Windows 2003 R2 server.
Client application running on a mix of Windows XP Pro and Windows 2000 PC's.
We are getting intermittent errors that boot the customers out of our
application. These errors are primarily networking errors.

The System Event Log has this entry:
The description for Event ID ( 0 ) in Source ( .NET Runtime ) cannot be
found. The local computer may not have the necessary registry information or
message DLL files to display messages from a remote computer. You may be able
to use the /AUXSOURCE= flag to retrieve this description; see Help and
Support for details. The following information is part of the event: Unable
to open shim database version registry key - v2.0.50727.00000.

Followed by this one which pertains to our software:
Faulting application taxtools.exe, version 4.1.0.0, faulting module
kernel32.dll, version 5.1.2600.2945, fault address 0x00012a5b.

It's always the same, first the .NET error then our software error. We used
VB 6.0 to create the software and do not call any .NET functions at all in it.

When we remove the .NET 2.0 from the client machines, it seems to run
better. But I have .NET 2.0 installed on my computer and have no problems
within my network like this.

The IT department at the client site state that the differences in the
networking components between Win2003R2 and Win2000 Adv Svr are probably to
blame. But as of yet, I can't find any documentation stating the differences.

Ideas? Suggestions? Help?