Software Deployment

I am trying to update an application that was deployed with a Visual Studio Setup Project. The project contains several classes with custom actions that are called on install/uninstall. In my update I simply copy over the new dll's and exe files into the application folder manually. This works fine as long as i dont replace any of the classes that contain the custom actions. However if I do replace one of the custom action classes, the application runs fine, but when I try to unistall it, it gives a "BadImageFormatException"

Is there maybe some registry entry that I could manually update to account for the change? Any suggestions would be appreciated.

Thanks
summer