PostSharp 3.1.49 may prevent you from debugging a library by way of not making a .pdb file next to a .dll file.

POSTSHARP_CONSTRAINTS;SkipPostSharp;POSTSHARP_CONSTRAINTS

...needs to go under the "Conditional compilation symbols:" under the "Build" tab of series of tabs one gets when right-clicking upon a project name in Visual Studio 2015 and picking "Properties" from the menu which appears. This will replace the .pssym file next to the .dll with a .pdb instead!

 
 

Addendum 5/11/2016: Please note that this will sabotage the ability to use aspects!