Good insight Frank!

That might be it, 'cuz I have to verify that the new user_ID provided for the new record (in the users table, as a matter of fact) doesn't already exist, so I do a count for id_user = newID, but in another workarea, like so:

&&llCree is a form-level public variable indicating that the user is creating a new record...
IF NOT llCree
    IF LASTKEY() = 27 
&&traps 'escape' key to be able to proceed with the cancel property of my quit button
	RETURN .T.
    ELSE
	IF EMPTY(this.Value) &&no username specified
	    mssErr("Veuillez indiquer l'identificateur de l'usager.")
	    RETURN .F.
	ELSE
	    lcAlias = ALIAS()	
	    USE usagers AGAIN ALIAS us IN 995
	    SELECT us
	    COUNT FOR ALLTRIM(id_user) = ALLTRIM(this.Value) TO liResul
	    USE IN 995
	    SELECT &lcAlias
	    IF liResul > 0
		mssErr("Cet identificateur est déjà utilisé par un autre usager, veuillez en choisir un autre.")
		RETURN .F.
	    ELSE
		RETURN .T.
	    ENDIF
	ENDIF
    ENDIF
ELSE

that code is in the valid event of txtID_user.

after verification in the debugger, the pointer doesn't move, in the concerned workarea, at least... Are the changes commited if I change the current workarea?