Why has this occurred The file “iTunes Library.itl” does not appear to be a valid iTunes library file. iTunes has created a new iTunes library and renamed this file to “iTunes Library (Damaged)”.

The library file appears to have been corrupted. You say you use your external drive but is the whole library on it or only your media? No matter, you will have to rebuild the library file:

iTunes: How to re-create your iTunes library and playlists - http://support.apple.com/kb/ht1451

Hey Friend. This same problem has just happened to me.

My entire library was on an external RAID. Just upgraded to 10.10.4 and got the notice my library file is damaged. I tried to the instructions on that link, but it didn't work. I think the .xml file was already over-written and blank.

Any ideas? Can i un-corrupt my file somehow? All the media is still there in the iTunes media folder, but i don't want to lose all my playlists...

Your playlists are in the .itl file and also in the .xml copy of the file. They are nowhere else (except on any backups you have, or on earlier versions which may be in the previous libraries folder). There isn't any method for un-corrupting the file (which is why we make backups of files we value).

When iTunes tried to open the damaged file, it created a new iTunes library and a new XML file. Or at least i think thats what happened.

I back up my computer just not the external drive. Any other ideas?

Here is the craziest part... when i open the new Library, very briefly under "Music" all of my playlists show for just a second and then disappear.

That's odd behavior. Perhaps the main library file isn't corrupt after all, or maybe it is but the second part is affected. I don't know much about RAID setups. I do see all kinds of weird behavior reported here in connection with NAS usage.

RAIDs can fail too. it needs a backup.

I had the same problem after a recent update. It took me a long time to figure out how to fix it, but finally did. It turns out the iTunes update was corrupt. I would copy a non-corrupt copy of the library.itl file from TimeMachine, put it in my music folder (on an external drive), open iTunes and voila! My whole library with all playlists, etc. are there. Then, after quitting and restarting iTunes I'd get the exact same corrupt file message and iTunes would create a new, empty library file. The way I resolved this is as follows:

Quit iTunes

Remove iTunes from Startup Items (if there). This is under system preferences (Mac), Users

Restart computer

Delete iTunes - I mean everything EXCEPT what is in your Music folder. Keep everything in the Music folder (whether in the default location or not)

Go to Apple's website, find the full download of the current version of iTunes, download it

Install iTunes, don't open it

Go into your "previous iTunes libraries" folder (in your music folder), change the name by removing the date, and move it to the Music folder, replacing the default library.itl file. Alternatively, go to Time Machine, find the last library.itl file before the corrupt update (in the Music folder) and move that to your current Music folder, replacing the one there.

Hold down option key and open iTunes

In the popup select "Choose Library"

Navigate to your recovered library and press enter (or open?)

iTunes should open with all your playlists, etc. Try restarting iTunes to make sure this worked. If not, cry.

Add iTunes to your Startup Items, if desired

Voila. Problem solved. (Well, at least it worked for me.)