I have this problem often, esp. with props. Its been discussed before in this forum and we reached the conclusion that it probably had to do with running Windows ME or 98. Whats your OS? Maybe its time to update. You could also try to get a RAM recovery app like RAMpage or MemTurbo, and recover memory just before you do a render. Since installing MemTurbo I get fewer render troubles. Actually I dont think Ive had this particular problem for several weeks.