Reports giving exception initting query error

When we save a adhocView, wich is based on another adhocView (via the save as method in the editor), some of our customers are getting a

java.lang.RuntimeException: exception initting query error.

The reports haven't changed in a couple of months... and this is the first time we encountered this kind of behaviour in the total runtime of our application. We are running jasperserver 4.7

Greetings,

Peter