Itunes ?

OK Sd, if it were me I would take the external HD back to the original Mac and run a repair utility on it. Use Apple's Disk Utility if that's what you have. There is a chance you can save your music.

If you're using Disk Utility and it doesn't seem to do anything the first time, repeat the repair process a few times. BTW the big gun in repair programs is DiskWarrior, but it costs.

Post number 7 in this thread will be of interest. Perhaps the problem is OS-related, triggered somehow by the update you did, and is not a problem with the drive itself.

If the problem does end up appearing to be drive-related, as indicated by the presence of similar symptoms when it is connected to different computers, if the drive is formatted in FAT32 and Toby's good suggestion does not resolve the problem you could try connecting it to a Windows computer and running the Chkdsk utility. Post back if you'd like further information about that, indicating which Windows OS is being used. I have found Chkdsk to be very effective in repairing corrupted disk file systems, which may be what is causing the problem.

Regards,
-- Al

Good advice from Al. One thing to try before you go either my route, above, or Al's, is unmounting the external disk (drag its icon to the trash or use the Eject button), then reconnecting it to the computer. See if the same message comes up. Sorry I didn't think of it earlier.

Do post back with an update if you get the chance.

Ok guys. I have tried a few things so far. The HD shows up on the desktop but not when i look for it as a new library option.
I tried the disc utility a few times. It didn't work. I tried it on 2 different Mac computers and it says the same message on both.
I will try to do the time machine backup to see if i revert to before i made the update to the latest version of itunes, if that works.
Luckily i did transfer all the info to a new HD just the other day.
Refresh my memory, when i add the new HD, do i just "add file to library"?

If your new HD is a duplicate of the one that's troublesome, and the troublesome one was you main iTunes library disc, then it should have an iTunes library on it.

In that case, hold down the Option (Alt) key when you click to start up iTunes in the Finder. When the "Choose iTunes Library" dialog appears, click "Choose Library...". In the window that appears, navigate to the new HD, find the iTunes library on it (just selecting the iTunes folder should be enough) and click "Open".

You should then have all your music available.

Good luck! Any other questions, or if this doesn't tell you what you want, please post.