My DNN app keeps throwing "Server Application Unavailable"

And I don't really know how to debug it......
Any ideas?
If I run it in the debugger from VS it tries to load the application for about 5 seconds than the aspnet_wp stops unexpectedly and the debugging process stops
and than that's it...
so I'm not really sure 
All I have to go on from the output log is

Ignoring managed exception from unknown thread.The program '[944] aspnet_wp.exe: Managed' has exited with code -2147023895 (0x800703e9). Ignoring managed exception from unknown thread.The program '[944] aspnet_wp.exe: Managed' has exited with code -2147023895 (0x800703e9).



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