"Undo" chrashes

EI am working on a rather complex scene and i have this huuuuuge problem. everytime i try to undo something “CTRL Z” Blender chrases. It ahs happend some times before when i nwas working with complex cenes. Does annyone know why this problem occurs?

how much memory does blender say it’s using?

can you tell us more about the scene? are you messing with armatures? node materials? particle effects? how many faces? objects?

and your computer… you’re in windows? how much ram? what graphics card?

Im using a WinXP computer. Im using abunch of noded materials and im using armatures, A highres HDRI and the scene contains 32596 vertices, 30590 faces, 722 objects and it uses 11mb of ram.

teh computer im using is a :
AMD Athlon xp 2200 1,8ghz
512 mb of ddr 400 RAM
Nvidia Gforce MX 440 128MB

eeh… wiiierd. I was working n the same project in the same scene with extreme caution and i was adding a bunch of objects. and suddenly i acidentaly pressed CTRL Z and it worked!!! wich it did not when i wrote the previous message. The only real change wich i think may have something to do with this is the fact that i had a sun light wich was layer limited. The one tine when this happend before i allso used a area lamp with a layer function and that is the only real significant similarity between the tw projects. but i find it hard to se why that would cause this kind of crash.