The save internally etc dialog is about wether or not image texture elements should be saved within the .car file or just kept as a path to the file on your drive. Internally takes up more space but save having to maintain all the image texture files on your system for the future. The only thought on this is that once when I saved files everything went as expected but in reality I had run out of disk space. Carrara 2.1 on winxp reported no errors and none of the files were actually saved. I only discovered the problem when I exited Carrara. I lost hours of work.