The value of the Project attribute in the <Import> element is not valid in VS2012, but works well in VS2013

Question

I got the following error while trying to load a project using VS2012.

 error : The value "" of the "Project" attribute in element <Import> is invalid. Parameter "path" cannot have zero length. 

I checked the code and thought that an error might occur, since VS2012 does not recognize the "EnvironmentConfig" variable:

 <Import Project="$(EnvironmentConfig)" /> 

I tried this answer which said to install or uninstall StyleCop, but that did not work for me.

In fact, I and one of my colleagues are checking the same source code, and it uses VS2013 without any other programs, such as ReSharper or StyleCop, and it can run the exact same project correctly.

Any tips? And also how can I check the value of $ (EnvironmentConfig)? I do not know where this is defined.