AO Render's Dying Not even halfway..

Ok, so I was rendering something the other day, and when I rendered in Blender Internal AO. With samples at 12, it crashed not halfway through! I loaded it up again, and opened up task manager, I looked at the mem usage, and for a while it climbed shallowly but steadily, then, right after a “box” was filled in, it began to move on to the next box, and the mem usage went from 68,000K to 128,000K (approximate values) does anyone know what’s going on? I currently am using Yafray at Medium full GI as a temporary fix.

What version of Blender are you using?

I’m using 2.45

Today I tried again, and now it didn’t crash, but my AO renders are taking literally 500 times longer than they did before, I could usually render in under a minute, but now I’m rendering above 6 hours…