I faced it today with VS2013.
Goto Tools –> Options –> Debugging –> General –>
Scroll to the bottom for “Use Managed Compatibility Mode” and Select the option.
Screenshot from the blog(url below):
Restart you debugging.
What Helped Me is below!
Visual Studio 2013 Could not evaluate Expression Debugger Abnormality
turned out to be very helpful.Also, you could see @Dreamers answer Unable to debug managed code using visual studio 2013