sysprocplan and sysprocauth locks

We are running a large production system against an Informix database, and have logged serious problems where a large portion of our user community will simultaneously get -211/ISAM -154 errors with the lock timeouts occurring on the sysprocplan and sysprocauth tables. At the time the users get these errors, they are running stored procedures. The onstat utility usually shows several locks (one hundred or so not uncommon) on the sysprocplan table. In normal day to day usage, the users run these same transactions, hitting the stored procedures all the time with no problems. This issue has been logged with Informix Regency Support, issue #403632. We are running an HP K400 server with 2 cpus, 1280 megabytes of RAM, and Informix 7.11UC1X2. The operating system is HP-UX 10.00. Does anybody have any experience with similar problems? So far we have been completely stumped... R/ Jon McNeill jmcneill@aimnet.com