In the form editor... select the field. Ensure the properties dialog box is
open (if not, right click on the field and choose 'Properties'). On the
'Event' tab of the properties, find the 'Before Update' choice, and click
the down arrow of this box and choose [Event Procedure]. Then click the
button beside the box (with the three dots on it). The following will come
up;
Private Sub Field_Name_BeforeUpdate(Cancel As Integer)
End Sub
Now, the code can be a little different, depending on the data type of the
field (and the field name), so you may want to try something like;
Private Sub Field_Name_BeforeUpdate(Cancel As Integer)
If IsNull([Field Name]) Then
MsgBox "Please complete this field"
Cancel = True
End If
End Sub
Alternatively, you could edit the table definition (if this field is from a
table, instead of a text field) and ensure that the 'Allow Zero Length'
property is NO and the 'Required' property is YES....