MS Access SetFocus not working on AfterUpdate event

Question

I have three related fields on a form: a textbox for a date to be entered [Qtr1Date1] and two comboboxes with reason choices [Qtr1Date1Reason] and initiator choices [Qtr1Date1Changer]. When the user changes the date textbox - I have the AfterUpdate event changing the color of the comboboxes and blanking them out. I would like the user to be directed to selecting a choice in each one (to update the audit trail) and not being able to proceed until doing so. I have looked at several other posts about the SetFocus not working, and order of key choices, but I am not sure why mine is not working. I am able to click on other fields on the form.

I have tried: -Entering blanking out in BeforeUpdate instead. -Validation Rule for combobox of Not Null (does not recognize initial blanking out) -Adding another control to setfocus to cancel order key events and then setting back to desired set focus control

Private Sub Qtr1Date1_AfterUpdate()
     Call LogChanges(StoreCode)
     Qtr1Date1Reason = ""
     Qtr1Date1Changer = ""
     Qtr1Date1Reason.BackColor = RGB(244, 66, 113)
     Qtr1Date1Changer.BackColor = RGB(244, 66, 113)
     Me.Qtr1Date1Reason.SetFocus
End Sub

Update: What I have done now to workaround not knowing how to make them enter a choice, is changed the reason and initiator to "Accounting Error" / "Accounting" and then entered a validation rule in those those fields that an entry must be made if there is a date, so they either choose themselves as the culprit or make another selection.

Private Sub Qtr1Date1_AfterUpdate()
     Call LogChanges(StoreCode)
     Qtr1Date1Reason = "Accounting Error"
     Qtr1Date1Changer = "Accounting"
     Qtr1Date1Reason.BackColor = RGB(244, 66, 113)
     Qtr1Date1Changer.BackColor = RGB(244, 66, 113)
     Me.Qtr1Date1Reason.SetFocus
End Sub

Answer 1

Original Validation Rule was testing for Null. Code was setting combobox to empty string and empty string is not same as Null. To resolve issue of "does not recognize initial blanking out" try setting comboboxes to Null instead of empty string.

I don't allow empty strings in fields.