Thanks for the reply.

I know that the disc is okay, as it's been recently used to upgrade a friend's DVD drive. Theirs is fine. The disc is perfect - no scratches or anything.

Can I check the actual contents of the disc for what version it shows, any particular file?

Also, do you know of a good place to find a <v21 copy? I've looked at the links on the site, but the ones for OS updates I probably need no longer exist And google isn't much use either.

Sorry to be a pain...