This only started happening recently, and I have no idea what's going on. I'll make changes to a form in the designer, compile and run, no problem. Then i'll go back and make more changes in the designer, compile, and it spits redefinition errors at me. For some reason, the designer is generating duplicated code. So far this has only happened to me while editing menu items and toolbar items.
EDIT: I should also mention that if I try and remove the redefined lines, the desinger gives me either a "C++ CodeDOM parser error" or a "Catastrophic error".