Thanks for the input guys.

You may be right about the multiple records but before I left here on Friday I ran a test update and entered a bogus but easily identifiable value for the field and despite saying 1507 records updated, the full 1587 records were updated with that value. Very strange unless SQL does not count the multiple records with an update.

Anyway, unless I can think of a way of discovering anything else that may play a factor in this the records I wanted to update have updated correctly.

Cheers again.