Which version of Visual Studio are you building with (if any)?
Which version of the WiX Toolset Visual Studio Extension are you building with (if any)?
Which version of .NET are you building with?
If the problem occurs when installing your packages built with WiX, what is the version of Windows the package is running on?
Describe the problem and the steps to reproduce it.
If the pseudo-wix.exe crashes with an unhandled exception, all detail is lost to the ether:
d:\path\to\wix.targets(625,5): error : An item with the same key has already been added.
Describe the behavior you expected and how it differed from the actual behavior.
If source-line-number info is available, it should be reported. Exceptions should include the stack trace, if only for the sanity of WiX developers. This should be true for all instances of the WiX "program."