Cannot create indexes

We are having problems creating indexes on several tables. We can get an exclusive lock on the table and there does not appear to be any other programs accessing the table but we receive error 242 242: Could not open database table (udba00.it_daily_mvmt). 106: ISAM error: non-exclusive access. Error in line 17This happens very infrequently but it not consistent either. Sometimes the index builds work fine and sometimes they don't. One weekend we even had 50 out of about 120 servers where the index build failed for some unknown reason. Are they any Informix bugs or maybe some other possibility than another program locking the table? Any ideas would be helpful. Thanks. P.S. We are running Informix Online 5.01 on NCR 3450 OS 2.01. Russ Ford brford@xmission.com