[Admins]

I don't see problems in the concent, but in the implementation:
Bad is the usage of

screenheight-=1

That will cause problems for the compiler, I guess you meant "screenheight - 1" ?
The "triggeraction 0,0,serverside,-GUI;" should be moved outside the timeout so
that it doesn't lag the game, e.g. if (playerenters) triggeraction 0,0,serverside,-GUI;