I also got this error just yesterday (and before) even thou there is plenty of space; What I found is that it was very large Poser file that I had just done a lot of 'tweeking' on, also I think I forgot to SAVE before attempting to render..... Reboot and all was well. You may also get the message that it is now Unable to Save the project after getting this error, and yes, after rebooting you'll be back to the "last save" and loose all else since. I think it's mabey more a Windows thing than a Poser thing, but....