you must create a timer control app level and timer event call login form. like this (in main prg):
DEFINE CLASS repeat_login AS timer
Height = 23
Width = 23
Interval = 60000 && 1 minute
Name = "repeat_login"
PROCEDURE Timer
this.interval=0 &&prevent continue
a=INPUTBOX("pass","Reenter password")
IF EMPTY(a) or a<>var_having_password
MESSAGEBOX("Don't have access",48,"Error")
this.interval=60000
RETURN .F.
ENDIF
return .T.
ENDPROC
ENDDEFINE
in every form you must restart the interval for repeat_login timer = 60000 to make sure the time to wait, using init or mousemove events.
if user doesn't open a form the timer will fire.

hope this help