[KevinH]

Your OS should be telling you when there is no disk space left. The error messages from attempted file IO just indicate that the request failed. There is no equivalent for "disk full" just an io error, as there is for "running out of memory errors". Lacking disk space for temporary files will result in many types of file io errors and cache file errors none of which will tell Sigil that your disk is full. Your OS should be warning you of that.

Next, Sigil does NOT ever touch the epub you load until you try to "Save". There is no automatic save in Sigil for just that reason. So if you did not attempt a save, there is no way Sigil can or will corrupt that file. So if your epub was corrupted, that means your disk drive is probably corrupted. You should run the equivalent of fdisk on it to test and repair your disk drive.

If you plan on using Sigil in the longer term, might I suggest given how cheap disks are, you upgrade your system disk drive as Sigil makes active uses of caching and temporary files, even to Save as it must have enough space to write out every file to a folder that is then zipped up to create an epub.