a lot of user seem to have trouble caused by antivirus software damaging the archives during downloading (real time filter) or extracting (damaged .scs files). Disabling the antivirus has been the solution for several user as well. IMO the Self-Help Guide should contain this important information; the hint is just missing:
Corrupted files
If you get an error saying the files are corrupted this is 100% false. It's more than likely to be one of the following problems:
1) Your archiving software is outdated and cannot extract LZMA-32 archives.
2) You're trying to extract files which aren't in the same folder, all .7z.00x-files must be in the same folder.
3) One or more files are not named sequentially. All files must be named promods-vXX.7z.00x. You may not have files like promods-vXX (1).7z.00x.
4) One or more files are missing or incomplete. Please use the file tester to verify.
So you should >>>Link<<< it.
Best regards