Dirt block texture completely fills up the screen, followed by a CTD

Pretty straightfoward. I load a map, play for 20-30 seconds, then screen is completely filled with the dirt block texture. 5-10 seconds later it crashes to the desktop. I've been playing Minecraft for quite a while and I haven't come accross this issue yet. I've played 1.4.2 Vanilla for a few hours without a hitch.