When I logged on today as admin, the icon for the administation was missing. Hovering over the screen I could select the invisible icon and clicked
"settings" or “users” or “help”. Both led to the error below. Anything else seems to work properly.
What do I need to do to get rid of the error? Any help is highly appreciated 
Just checked: I have upgraded to NC 13.0 in Februrary. Everything went fine.
Internal Server Error
The server encountered an internal error and was unable to complete your request.
Please contact the server administrator if this error reappears multiple times, please include the technical details below in your report.
More details can be found in the server log.