Struggling with ADO

Hi all, I'm using VB6 with ADO to connect to an Informix 7.20 SE database using Merant's (aka Intersolv's) OLE DB provider for Informix. I create a recordset ok, but when I use the Update method to modify a row, it appears that the darn thing is trying to sequentially lock every row in the table. My test table has 100,000 rows in it, and there is a very long pause on invoking the Update method before control returns to the program. If I lock another row in the table (using the Update command in a sperform screen), the driver returns an error about "cannot lock row for update", even though the locked row is not the one being updated by ADO. If the row locked by sperform is near the beginning of the table, the error comes back immediately; if near the end of the table, it takes several seconds before the error comes back -- as if a lock is being attempted on every row in the table sequentially. This happens even if the row locked by sperform is not included in the recordset. The table in question does have a primary key, which is included in the recordset fields. Any ideas? Thanks in advance, Ed Brown