If it is happening for only a few users then the problem may be caused by security conditions built into the query. However, you need to give us some information about the SQL the workbooks are running. Do you get this error even for the very simple queries?
I would suggest grabbing the SQL that has been generated for the workbook and then running it against the database manually. From there you should be able to figure out where the problematic subquery lies and the data causing it.