It would help if you'd give the context in which you're seeing the
error. If it's produced by code (which is likely) then a short but
complete example would help. See http://www.pobox.com/~skeet/csharp/complete.html for more details about
what I mean by that.
Basiclly I have wrote some code which checks a number of inputs (to be used
in a Biztalk 2004 Map). Within Biztalk I got the following error. But I have
solved the issue. Their was a field that had been left null and this is why
it was throwing the error.