Try breakpoints where you suspect the 'error' is happening. If you don't have an idea of what section it is happening, you can use 'single stepping' through the entire code.
As this happens on a target machine then i have build the setup project, unistall the previous and so on... not that easy

By the way it would be nice if someone tell me how to build a setup project that automatically removes the previous one, using setup and deployment of VS.NET not those third party programs.
Ok , paste this code where you expect the error fires.
I have seen that post before and i was going to search for it and use it, thank you ,but i am almost sure it will return "Don't Know why I'm closing!!??"