You cannot use the Valiation Rule of the text box on your form, becuase the
rule will never be tested if the user never types into the box.
The simplest solution is to:
1. Open the table in design view.
2. Select the field.
3. In the lower pane, set its Required property to Yes.
You can use the Validation Rule in the lower pane of table design if you
prefer. Just type:
Not Null
If you want to warn the user the field was left blank, but allow them to
save the record anyway, use the BeforeUpdate event procedure of the *form*
(not control.)
