Last week I had an issue in Visual Studio 2010 debugger in some projects only! When I was looking at the value of variables I was getting an error message saying “Unable to evaluate the expression”!
Searching on Connect I have found that someone else had the same issue! Not really a good sign, “Debuging (Evalutation) stops working at times - Unable to evaluate the expression”. I have the same configuration, same issue and can reproduce what is described: