Thanks DCrake,
I copied your nz function in and got a halt indicating [Intv] in the From statement could be ambiguous so I changed t0 the followiing:
IIf(Nz([tblTrainingLog].[Intv],0)=0,Null,DateAdd('yyyy',[tblTrainingLog].[Intv],[DateTrained]))
It didn't give me a halt, however, it didn't...