Depending on the tone of the application you can use something like:
"Oops! Something went wrong." - Send error report to help us improve your experience
"The application has encountered an unknown error." - Send error report for diagnosis.
Google chrome uses a generic error: " Google Chrome quit unexpectedly." - Ignore, Report or Reopen.
You can follow up the dialogues with whatever preventive measure you took, "The system needs to shut down" "The service restarted" or whatever fits in context.