Error 229 - ISAM Error 113

We recently upgraded from Informix-OnLine 4.00 to the 5.01 (Unix-based) engine. A "new" error is popping up intermittently: 229: Could not open or create a temporary filecoupled with: 113: ISAM error: the file is locked. This seems related to the temp file being created during a query (run from the command line by ISQL 4.00.UD2). It is definitely not caused by file-permissions nor by lack of space in the DBTEMP directory. It occurs in select-only queries as well as with updates or inserts (or whatever--there's no pattern apparent yet). We've been wondering if this might be caused by some underlying configuration problem. (We have one dbspace divided into three chunks. They are 77%, 49%, and 75% full, and these sizes do not appear to change during the above-mentioned error(s).) Might this have to do with some hook which is not being released consistently? Any ideas or suggestions gratefully accepted. Thanks. -- margaret@srs.ahs.state.vt.us