>>>> Solution: Reboot!
A restart of Visual Studio IDE probably has worked as well.
Note, the Visual Studio caches some current project status information in .ncb file. That cache only will be actualized at a new pogram start. When the above message comes timestamps of the last build do not map to the information stored in the pdb file. As far as I found out in similar cases, the issue could be solved by quitting Visual Studio and restart again. Of course a reboot would make a quit as well ;-) But, I also had cases where I had to delete all temporary project files, especially .ncb, .aps, .pdb, .ilk, before the error was gone.
