Are you publishing something different to the screen-a flash file or the like?
If not..
then it sounds like you may need a re-install of the client software on the screen, although if you were using the EWF function than in theory nothing should have changed in your client installation to cause this error.-You could set the screen to auto update the client software from the server each time it starts, this should then (hopefully) fix it for you.
EricL