When I try to run the project it says:
Error while trying to run project:could not load file or assembly \'Project.exe\' or one of its depend
The module was expected to contain an assembly manifest
It is a low-level assembly loading problem. The CLR has located a file with the right name but when it tries to load the assembly, it finds out that the file doesn't contain a proper manifest. A .NET assembly must contain a manifest, it contains metadata that describes the assembly, listing the types in the assembly, etc.
If you have no clue what EXE or DLL might be the troublemaker then you can use the Fuslogvw.exe utility:
Several possibilities, a common one these days is to trying to load a .NET 4 assembly with an EXE that asked for CLR version 2. That requires an app.exe.config file that forces CLR 4 to be used.