I have installed VS 2015 RTM (nothing else) and I\'m unable to debug any solution, not matter if it\'s an existing one or a brand new one (created with VS 2015 and compiled
In my case it was due to the project Target platforms were different.
Consider : ProjectA (Entry) --> ProjectB
ProjectA's platform in properties was set to x64. And ProjectB's platform was 'AnyCPU'.
So after setting ProjectB's target platform to x64 this issue got fixed.
Note: It's just that Target Platform has to be in sync be it x64 or 'Any CPU'