Get "Internal Error in the Expression Evaluator" on "Add Watch" Function When Trying to Debug Wcf Service Code (Msvs 2013)

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

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/

Internal error in the expression evaluator

That sounds like a bug in the expression evaluator. For a better workaround, instead of checking "Use Managed Compatibility Mode", check "Use the legacy C# and VB expression evaluators". This should enable you to continue using Edit and Continue as well as other features added within the last few releases.

In terms of the "Internal error in expression evaluator", can you please open an issue by going to Help -> Send Feedback -> Report a problem? That will help us fix the problem in future releases.

Visual Studio mouse over debugging doesn't work for particular variable

I figured it out. It was grayed out because I was currently debugging. Once I stopped the process it was available to check.

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