Found the log!
McAfee\ePolicy Orchestrator\Server\Logs\ Orion.log though it really does not tell me lot.
Are you able to try the query within SQL Management Studio or equivalent SQL client?
In addition you might want to copy here the really relevant section from orion.log at the time of running ePO query so others can see and advise upon.
If the query is for a product that no longer has an extension checked in I could see this happening. For instance, if you have a query for VirusScan 8.5, then you removed the extension, this query won't work properly anymore. Can you create a new query with the same criteria as before?