Viewing Forms [Design] mode

I packaged my application and everything went fine, but now when i go back into VS and try and look at my forms from the design view it throws this error.

An error occurred while loading the document. Fix the error, and then try loading the document again. The error message follows: The format of the file 'Outsource Rebate Checks.msi' is invalid.

What could cause this and what can I do to fix it.

Thanks in advance.

i don't know what causes it but it surely runs, right? though don't have design mode. i did adding new item and copy paste the code. but i know it wasn't a good idea, any better than mine would be greatly appreciated. thanx...