Create a NEW singleinstance codeunit. This codeunit you have to launch in Codeunit 1 FUNCTION LogInStart(). Globals :

recUserSetup : Record : "User Setup"
autTimer : Automation : 'Navision Timer 1.0'.Timer (property WithEvents=Yes)

OnRun() of your singleinstance codeunit:

IF ISCLEAR(autTimer) THEN BEGIN
CREATE(autTimer);
autTimer.Interval(3 * 1000); // test each 3 seconds
autTimer.Enabled(TRUE)
END;
CLEAR(recUserSetup);
IF recUserSetup.get(USERID) THEN ;

On Trigger
autTimer::Timer(Milliseconds : Integer)

IF TODAY <> WORKDATE THEN
IF NOT recUserSetup."User May Change WORKDATE" THEN BEGIN WORKDATE := TODAY;
MESSAGE('You may not change the WORKDATE. WORKDATE has been resetted');
END;

Create a New singleinstance codeunit. This codeunit you have to launch in Codeunit 1 Function LogInStart(). Globals :

recUserSetup : Record : "User Setup"
autTimer : Automation : 'Navision Timer 1.0'.Timer (property WithEvents=Yes)

OnRun() of your singleinstance codeunit:

IF ISCLEAR(autTimer) THEN BEGIN
CREATE(autTimer);
autTimer.Interval(3 * 1000); // test each 3 seconds
autTimer.Enabled(TRUE)
END;
CLEAR(recUserSetup);
IF recUserSetup.get(USERID) THEN ;

On Trigger
autTimer::Timer(Milliseconds : Integer)

IF TODAY <> WORKDATE THEN
IF NOT recUserSetup."User May Change WORKDATE" THEN BEGIN WORKDATE := TODAY;
MESSAGE('You may not change the WORKDATE. WORKDATE has been resetted');
END;