Me.LastModifiedTxt.Text = Format(Now(), "MM/DD/YYYY") would not be a problem on an unbound form so I'm not sure it's the problem here. However, by not using the Text property, you can avoid having to set the focus to the control.
I question why format Now when you can just write the date? Since the error message can also apply to violation of a validation rule, is it possible that the field isn't date/time or the result of the expression violates such a rule?
I also wonder if the control given the focus is part of the same record (which would be in edit mode due to the combo update), or if there's a form/subform setup involved here. The violation could also be related to a subform record problem.
EDIT
text property may or may not be a vb.net property, but it is certainly a vba property. In a bound control, .Value is the last saved data, .Text is the current data displayed in the control. If you leave the control, the .Value property becomes what the .Text was.
Last edited by Micron; 11-23-2018 at 11:21 PM.
Reason: added info
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.