Vermutlich durch Windowsupdates hervorgerufen.
Dies hat mir geholfen:
http://lookatgame.com/view.php?video=c8YwOlCQipU&feature=youtube_gdata_player&title=GTA+4+rmn20+Error+Fix+%2A%2A%2A%2ANO+DOWNLOAD+NECESSARY%2A%2A%2A%2A (http://lookatgame.com/view.php?video=c8YwOlCQipU&feature=youtube_gdata_player&title=GTA+4+rmn20+Error+Fix+%2A%2A%2A%2ANO+DOWNLOAD+NECESSARY%2A%2A%2A%2A)
Dann konnt ichs bei steam wieder starten.