Sorry you are having trouble. Spine downloads its update files to this location:
Windows: <user home folder>\Spine\updates\
Mac: <user home folder>/Library/Application Support/Spine/updates/
Linux: <user home folder>/.spine/updates/
After downloading, it checks to make sure the file is OK. If it isn't OK, you get the error you are seeing. I can't see any other reason why that would happen. 🙁 Are you sure there is no antivirus or anti-malware software that could be interfering? Could you try to disable such software (or whitelist the updates
folder above)? If you look in the updates
folder, do you see any files?