I have had this happen once before when building a (whoa nelly) 1000x1000 level.

(I didnt get too far )



The size of level you can run depends on, as it has been said already, your RAM.

One of my friends tried to play a rather big level on his old 133 and it came up with that error. I then tried the same level on my 350 and it worked fine. (I stuck in the proc. speed to show the age of the PC and I also thing the speed has a minor factor too)