The "save-last-image" parameter is kind of a safety net, if you haven't
set to render to file and discover that you like the image you've created. It
isn't necessary, and can be set to on or off in the 3DS.set file. The
Installation guide says…"Important: when this option is on large amounts of
disk space may be required". This is especially so for high-res images.
I suggest that you may inadvertantly be running short of room on your
hard drive. Check how much of a swap file is being created when you render, if
any, and compare vs. your free space on hard drive. You might need to do some
housecleaning, especially if you're keeping lots of test renderings and
tutorial flics. You might also check to ensure that you're rendering to some
sort of compressed file format as well.