Here is the control field (Note, I originally had it set to True with the same outcome)
=DLookUp("[Apiary_Active_Ap]","[T_Log_Apiary]","[Log_Apiary_ID] = " & [Forms]![F_Log_Inspection_Main]![Link_to_Log_Apiary_ID_Is])
I have always understood that the filed Name was the controlling identification versus the Control Source.
Is it different in this case ? I'll get a chance to try it later