Ok, forget last solution, I encountered the issue again and apparently am not the only one:
http://social.msdn.microsoft.com/Forums/en/vsdebug/thread/4f7b3eb5-67b5-4066-8299-fe7635cc1d82
Solution:
What finally worked for me was this:
Step 1:
Tools-> Options -> Debugging -> Symbols: Uncheck 'Load Symbols' (see below)
Step 2:
Right click solution --> Common Properties --> Startup Project: Set to 'Mutliple' and 'Start' (see below)
Learning is doing ...