I'd like to know what this message means as well. I can't seem to find the setting in Viewpoint that generates this alert. We also had no query running for the user at this time. There was a gap of a number of hours either side of the alert time when no query was logged for this user.
Oh - and I believe this error (generated by Viewpoint) to be reporting that a user ran out of spool since the last alerting time (in my case in the past 24 hours). I don't think it's alerting of a problem at the specific point in time. It might be nice if it also provided a time so you could look up the query!
You could search the DBQLogTbl for error code 2646 (No more spool space in %DBID).