Trying to run a test in VS2005 RC fails due to an 'Object is in an invalid state'
Dave had a problem yesterday while teaching a VSTS class in Illinois, himself and some of the students were getting a message box saying something like 'Object is in an invalid state' and the tests just wouldn't run. So Dave called me to see if I had seen the problem before and yes, I had seen it but disappeared on me after a VS restart. Well, I am in Redmond this week and Rob Caron pointed me in the right direction; after exchanging a few emails, about an hour later I received a response from the Test Tools team, namely, Eric Jarvi (Thanks Eric, for the quick response!) ...
Long story short: This is a known bug in RC and has been fixed in a later build.
The Solution: Close Visual Studio and delete your <solution>.suo file. This file does not contain any code, only user options and other information about the state of the solution in Visual Studio; and it is a per-user file.