> Does the error occur if you explicitly set KeyLinks?

I did try to explicitly set KeyLinks with identical results. IBO
correctly identified the key column and used for the searched update,
the problem is that the VALUE to search is zero.

> (and then just a little check to rule out plain stupidity: We're not
> talking about rows that have just been inserted and where the PK is
> assigned through a trigger?)

No, I only try to update an existing table.

Regards,

Eyal.