Hi Guys
Well thank you all for your help, I discovered the problem quickly after your posts. Was a typo really - got the format wrong.
Offending Dlookup: DLookup("ProcessLock", "TblRendesvous", ID = 1)
Correct Dlookup: DLookup("ProcessLock", "TblRendesvous", "ID = 1")
Thank You all once...