Assuming your problems are with the AVCHD (approx. 8 GB) release of RotJ, then you should find a checksum utility inside the directory. Hopefully this small program hasn’t been corrupted. Let me know if it has, and I’ll PM you a link to it. Have you tested the checksums of the ISO and MDS files against those provided in section 6 of the Ultimate Guide?
If the checksums match, all I can suggest is that you try a different extraction program. I use 7zip and have extracted all of Harmy’s stuff without problems.
If they don’t match, then go to the individual rar files you downloaded, obtain a SHA-1 checksum for each one, and PM me the details. I’ll compare them with mine and let you know which rar file(s) is corrupt. With a little luck you might have better luck downloading the problematic file again. Otherwise, I shall stick it on Mega for you.
Bluto
That’s great advice and I’ll follow it the best I can when I’m back with my laptop but I’m not 100% on what you’re talking about with checksums and all that. I’ll go into the file and try to figure it out but I’d appreciate it if you could explain this to me like I’m 5