MariaL
You may be missing a step here. For the before update event field property, create an event.
When in the field before update field, either click on the down arrow, or type "[e" to bring up "[event procedure]"
Now click on the "..." box immediately to the left of the field. This will take you to the VB editor. Type
me.fld_name = now()
and then exit the VB editor. (Note how the VB editor started to bring automatically brought up your field name when you typed "me." - hit the space bar to select variable or keep typing the name.)
ALSO
Since this field is updated whenever you create or edit the record, don't allow the user to edit it -- no point. Either make the field invisible, lock the field, set enabled to false using the field property.
Richard