Thanks for posting.
The description of the error code is displayed to the right of the server name. In this case, it's that the database couldn't be backed up because it's currently closed. You can find a list of FileMaker Server error codes here:
Thanks for the reply - the list of error codes will be very useful!
The description of the error code just told me the "operation" could not be completed - I suspected it was the backup from the time! I have bookmarked the list of error codes for future reference!