PushModalScreen called by a non-event thread

Hello,
I am a new java developer on blackberry and i have a push application
that works as a system module and runs at start-up. When i push a
message form server I want to see a pop up screen on blackberry
(suppose that the main screen of bb is opened when push message
arrives.i mean we are not in any application.) When i try this i get
en error like this: PushModalScreen called by a non-event thread. Do
you have any solutions for this?