Do Windows XP and Windows Server 2003 parse differently?

I have a curious problem with code that runs perfectly fine on my XP-SP3 IIS 3.5 development machine but crashes on my 2003 IIS 3.5 test server with a:
    System.FormatException
That should be a parsing error, but the only parsing is being done through TryParse, and any errors should throw handled exceptions.
I'm not seeing anything in the server logs that clues me in.
Is it possible to throw a FormatException that is not a parsing error?  Is there a method to get more information about the error so I can (at least) find what boneheaded thing I've done to cause it?
Thanks,
 - Tinker
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