can't initialize sort area

I've a colleague (a remote one though: he's with another company in the same corporation) who's running Informix 5.0 and Informix-ISQL 4.1 on SCO/UNIX 3.2.4. He has an ACE report that pivots on a SELECT statement that joins 6 tables and orders on several columns and thusly requiring some heavy sorting work. He's getting error -566 (corresponding error text says "can't initialize sort area", or some such, I am not sure). He tried the SELECT statement in ISQL itself and got the same error. He reduced the # of tables joined and was able to get pass it (but then also not getting what he originally desired, of course). He had made sure that: - $DBTEMP points to a place where there's definitely enough space for any sort temp. files - The logs are almost empty and there is enough space for the sorting work (he has only 1 dbspace) - The ulimit is at its maximum value and there's no permission problems Does anybody has any ideas?