Wish I had seen this before I reinstalled everything, remotely I might add. I was on a business trip in Japan when my wife complained MP would no longer run and gave this error. I had to log in remotely from Japan and reinstall a basic config of MP. 
Copied contents from configuration.exe.config file to the mediaportal.exe.config file and all seems fine.
Many thanks erron - I ran into the same issue in 1.2.1 (SideBySide Error ID 59) and MP would not start, after my power died and UPS battery was dead and system was not shut down (MP was still open and probably doing something!)copy the contents of conginuration.exe.config and paste that into mediaportal.exe.config and it should work, did for me.