Well the stack trace shows you where to problem likely is: You're using a tiled sprite that tiles very very closely, think 1 pixel. Each time there's a tile, it adds vertices and some other things which eventually will fill your memory. Unity is only 32 bit, which means that the editor only ever has access to 4 gb ram, so if Space also takes up a lot of memory, both together likely cause this. The reason it's NGUI that causes the error, is that Space probably allocates its ram use before the tiled sprite does.