.net - There is an invalid character ...

[kevina]

And now for the rest of the story (so the thread isn't left hanging):

The situation that was experienced here was that a symbol had been entered in the postbuild line of the .csproj file in the IDE, which made the resulting xml invalid, and the xml parser in Visual Build Professional was detecting this invalid xml and treating it as an error.

In this case the invalid character was a non-standard "-" symbol, which could safely (and appropriately) be replaced with a standard - character and all was well.