While you are developing an application with Visual Studio 2010 may occur the BadImageFormatException. That thing occurred also to me. I googled very much, but couldn't resolve the problem. Eventually I found the solution.
Now I suggest to you my solution:
Start a new project
In solution explorer right click on the project name and select "Add an existing item"
Load all files of the old project in the corresponding location of the new project, included the dlls