This is what ended up working for me, I put this in the field area of the query. Hopefully, this thread can help someone else. Thanks for steering me in the right direction guys!
WARNING: Nz(IIf(DCount("*","ISD_LIST_SUB_QRY","[ISD_LIST_SUB_QRY].[ID]=" & [ISD_DETAILS_TBL].[ID])>1,"Multiple...