Update prob. w/ I-SE logfile

Hi there, Env : SCO Unix 3.2v4.2 + I-SE 5.00.UD1 Table: mov ( year smallint, month smallint, nrdoc int status char(1)) Index: unique ( year, month, nrdoc) Transactions: on Users: Only me The problem arises when i try the following update: update mov set status = "A" where year = 1998 and month = 2 after a few seconds the engine returns errors: -346 - Could not update a row in a table -121 - ISAM error: cannot write log record I've tried doing this update: - with/without begin/commit - after unload/drop/create/load the table - after removing/creating a new logfile - after a "repair table" but nothing works, and the errors don't go away If i try: update mov set status = "A" where year = 1998 and month = 3 it works, what about that, and month=3 even has a lot more records than month=2, go figure. One thing that's strange is that the logfile seems to break arround 400K, but if i do several updates that extend the logfile above 400K it works alright. I suspect a record in month = 2 is causing this, but which one ? Does anyone have any ideas, sugestions, whatever ... i'd appreciate. TIA.