When I imported an old solution in VS2015 I receive loads of warnings MSB3884 warning: Could not find rule set file .. when building the solution.
Q
You need to edit the .csproj file and find the reference to the CodeAnalysisRuleSetDirectories
. Change the version of the Visual Studio reference in the path to the one that is for VS2015 (a.k.a 14) and reload the project. (That worked for me.)
Alternatively delete all references of
I found the solution here.