Visual studio 2013 CUDA 7.5 adding cpp files to project

Hi All,
I update my project form CUDA 7 VS2012 to VS2013 7.5 everything works well except that all the cpp files are not included in the project and when i am trying to add cpp files that were in the project at VS 2012 i get the following message:
the desired name for XXXX.cpp is invalid
The problem is that i cannot debug cpp files the are crucial for the project, i think the project uses the compiled file but they are not included in the project

Please someone help.
Should I just upgrade to 8 and VS 2015?

Since the error message is about .cpp files, this issue does not seem to have anything to do with CUDA, but with (the lack of) portability of MSVS .sln files across versions?

I anticipate that this is going to be unpopular advice, but it is good advice nonetheless in my experience: Avoid MSVS solution files, avoid CMAKE, use regular makefiles. Does wonders for programmers’ sanity. You get to specify directly how your code will be compiled instead of trying for hours to convince an intermediate layer to produce the desired compiler invocations for you indirectly.