I also have that error sometimes. Usually a re-boot of the system is the only fix. I try to save often, but if it happens it sometimes corrupts the file. But only if i try to save after getting the error. AND, it happens anywhere in C. Which brings me to thinking that it's all based on a memory problem, as in C doesn't drop old data when you've moved forward, until it fills up the system and there's nothing left to do the requested command, and crash. emell - I would HIGHLY suggest rendering out sequenced stills instead of a video file when doing animations. Use the batch option in the render room and then if there IS a crash, you can always pick up where you left off instead of having to start over. I also, if it's crunch time on a project, or if it's the final version, restart my system, start up C and only do the batch run so that there's no 'left-over' memory problems hanging that will screw things up. After you render out your stills, drop them into Premiere or Final Cut or whatever and compile the animation there. I once did an animation render that took over 54 hours to run! I left town, did some work for a client in another city, (calling my wife every now and then to see if it was still running!) and came back to find everything ran smooth as silk by following the above steps.