Hi Nadia

I used to find this problem with VFP3, with an order processing form displaying order items in a grid. There were several relations set to readonly and read-write tables from the order headers table. The read-write tables were all table-buffered optimistically. This is the fix I used:
=RLOCK("orders") && Header, displayed on form
=RLOCK("odlines") && Items, displayed in grid
=RLOCK("stylcols") && stock table, not displayed but updated
=RLOCK("styles") && read-only, displayed in grid
=RLOCK("colours") && read-only, displayed in grid
UNLOCK ALL

Note that checking the lock status on any of the tables gives a negative result. And of course with optimistic locking, nothing should have been locked anyway. The RLOCK() is essential - just issuing UNLOCK doesn't work.
I usually place this code in a method on the grid called .bugfix() <s>, and call it after any child tables ("odlines" and "stylcols") are written to.

HTH

ChrisM, London, still winter.