mspdbsrv.exe is the process Visual Studio uses to create .pdb files when you compile; these are the symbol files that let you debug an application. Sometimes it goes berserk and doesn't shutdown correctly when you exit Visual Studio. I've had this cause bad compiles even after quitting and restarting Visual Studio. Use [process explorer][1] or the task list (Ctrl+Alt+Delete in Windows) to manually kill mspdbsrv.exe if it's broken on you.
For what it's worth, I haven't seen this problem happen in Visual Studio 2008 as of yet, but I've only been using it a few days.