Hi,
it's always a good idea to have a backup of your data. You could make a
backup on close each time you have added new data or edited the data.
While you are experimenting with update queries, it is always good practice
to make a copy of the main data table before you use an action query
(update, append, delete) on it.

Another idea which would help save you from this sort of grief, is to work
out exactly how to do these queries to update the data and put them in code
on a form and use the form to do all your data changes.

Jeanette Cunningham

Perhaps you could open the query in SQL view and post it here. It would also
help to indicate what fields there are in your table, and how you're
determining which record should be updated.

If the criterion is JUST that the hours are NULL, you'll be updating every
record in the table with null hours, no matter what the date and the employee
ID might be, unless you're somehow indicating which employee and date you
mean!

            John W. Vinson [MVP]