I have .net application (GUI as well as PowerShell) built against 4.5. My OS is server 2012. When I attach my application to 2013 visual studio, the debugger is not working
You can resolve this error by applying below points
Sol 1:
1) Restart visual studio and re-open your project.
2) Open your project bin directory and delete DLL of that code where your debugger is not working properly.
3) Then again add DLL reference in the bin directory.
4) Remove all breakpoints.
5) Build project.
6) attach with one w3wp.exe process in attach to process window
7) Enjoy your problem has been resolved.
If above solution is not working then you can try solution that has been provided on bellow link
http://weblog.west-wind.com/posts/2013/Nov/21/Visual-Studio-2013-Could-not-evaluate-Expression-Debugger-Abnormality