Get “Internal error in the expression evaluator” on “Add watch” function when trying to debug WCF service code (MSVS 2013)

Question

Few days ago I moved my solution to MSVS 2013. It works fine except one thing: when I trying to debug code of my WCF service it works, but when I want to watch state of any

Answer 1

This might be a bug in the new (managed) debug engine that ships with Visual Studio 2013. Try turning on Managed Compatibility Mode (which effectively turns it into pre-2013 debug engine), located under Tools - Options - Debugging:

If this solves the issue, then I'd suggest trying to reproduce it with a small project, and then reporting it on Connect, so it could be fixed.

@bjhuffine comments below that there are other ways to enable compatibility mode, without globally disabling it (e.g. per-project). More information here: https://devblogs.microsoft.com/devops/switching-to-managed-compatibility-mode-in-visual-studio-2013/