问题
My Visual Studio 2012 installation has unexpectedly started to show the message "Unable to evaluate the expression" everywhere where we watch variables in debug mode.
I already tried to change some debug settings, as proposed by some fixes, but the problem stays there.
Some others fixes recommend us to re-install visual studio, which I wouldn't like to do. What more can we do to fix it ?
回答1:
A reset in all my visual studio settings using "tools -> import and export settings" (which allow you to save the current settings before reset).
After the reset my debug issue was fixed. Then I imported my saved settings and the problem stays fixed keeping all my original settings.
回答2:
I had a similar problem and in my case it appeared that several devenv.exe instances were running, which caused the issue.
来源：https://stackoverflow.com/questions/23763921/unable-to-evaluate-the-expression-in-visual-studio-2012-debug-mode