Using recordset option dboptimistic

Hello all-

I am probably overlooking something very simple, but here's my problem...

I am linking tables from Ingres using a DSN which is set for locking at the page level. When I open a recordset with:
set rec = currentdb.openrecordset("tablename", dbopendynaset, dboptimistic)
I get the message ODBC--Can't lock all records.

I also tried:
set rec = currentdb.openrecordset("tablename", dbopendynaset, , dboptimistic).
which resulted in a syntax error

What am I doing wrong?