cmid or courseid not passed to script??
Can't reproduce this error.
There are several ways to move questions - moving a whole category in the category page, using the checkboxes and the 'Move' button on the Question page. Or by clicking the move button to move one question at a time. Which way was causing the problem. I checked all of them and they seem to work OK for me.
Is the problem still occurring? Reopen and provide more info if this is still a problem.