OPC DA server stopped. The OPC Server terminated unexpectedly!
What OPC server is in use?
AC800? Check its log files (it keeps a handfull of the last session logs on disk before deleting the oldest)
Probably you should file a support case with your regional ABB support team.
The 800xA OPC DA & AE frameworks are continuously monitoring the health of the OPC connections that are in use. Sounds like the OPC server decided to abort itself. Most ABB OPC servers does this if all controller communications breaks down.