Hi. I thought I'd post this solution to the error 42408 problem after an iTunes 9.0.3 upgrade, as it may help someone else who, like myself, has found that none of the previously suggested fixes work for them.
The first thing to note is that, under preferences > advanced, iTunes now points the iTunes music folder to being Users/Username/Music/iTunes/iTunes Media, so your Library .xml file and any other Library files will have to point to that path as being the holder of your music rather than the old "iTunes Music" folder path. Basically, what I did was to move the whole iTunes folder and the various iTunes and 1 iPod .plist files under Users/Username/Library/Preferences to the desktop, leaving nothing behind. I then uninstalled iTunes. I then copied the contents of my iTunes Music folder from the desktop to the "iTunes Media"folder and reinstalled the 9.0.3 update. Then, I let iTunes go through its prompts asking me various things about what to do with iTunes, such as search the Home folder for music etc. and answered all the questions. I think this must update the Library information in the iTunes folder.
In any case, after I did all this I downloaded a script that some helpful person had developed for solving the iTunes error message at
http://megabytecomp.com/apps.aspx and I then unzipped and ran it and restarted my Mac. The script clears out the user cache folder. For some reason this seems to work. You have to authorize your iTunes music either at this stage or after you connect your iPod to your computer. But you have to follow a certain procedure when you attempt to synch your iTunes library with your iPod: First, open up iTunes from your applications folder and wait until it is fully loaded before then connecting your iPod. From there on in you should be able to synch your iPod and iTunes as before, except you will always have to first open iTunes from your applications folder and wait till it loads before connecting your iPod to your computer.
I should add that this was all done on an iMac with OSX 10.6.2, not under Windows. I noticed some Windows users are also having the same problem with iTunes. Unfortunately, the script I mentioned above is an .app so it would seem it is only usable on a Mac. But if you have some virtualization software running and are booting into both Windows and Mac OSX, you can at least, hopefully, use it with your copy of OSX.
Hope this is of some help. As I say, it worked for me, but it may not work for everyone who, like me, found that the other suggested solutions in this thread didn't work for them. One thing to keep in mind is that while I found following this method allowed the fix to "stick" and keep working after a restart of the OS, the site with the script on mentions that sometimes it can take several repeats of the procedure and using the script for it to finally "stick".
Like everyone else, I just hope Apple addresses this problem with iTunes and provides an update fixing it so we don't need these workarounds.
