Eftersom jag inte drabbades själv så har jag inte testat denna metod, som går ut på att radera iTunes databasefilen på din iPhone och börja om på ny kula /Freebo
1) On a Mac using Cyberduck or a PC using WinSCP, view the files on your iPhone (google SSH Cyberduck iPhone if you need help with this step)
2) Navigate to /private/var/mobile/Media/iTunes_Control/iTunes/ and delete the file iTunesDB
At this point, iTunes will no longer give you the error message BUT, your music, ringtones, podcasts will still be taking up space on your iPhone but your iPhone won't try to read them and iTunes won't see them. The solution is the next step.
3) In Cyberduck (or WinSCP) navigate to /private/var/mobile/Media/iTunes_Control/Music and delete all of the folders in the Music directory
4) Go back one level to /private/var/mobile/Media and go to the Ringtones directory and delete them too.
5) Close iTunes and open it again, allow your iPhone to sync again. It should copy all your music, podcasts, and videos back to your phone, though depending on how much you have, it could take a while.
6) If you have Ringtones in your iTunes and they're not going back on your phone after all of this, plug your phone in and select the iPhone in Devices in iTunes and click the Ringtones tab. Deselect 'sync ringtones' and it will display a message warning you that all ringtones will be removed from you phone. Accept that and click 'apply'. After the phone has finished syncing, select 'Sync Ringtones' again and click apply. Allow it to sync. That successfully put the ringtones back on my phone.