How i solved the iTunes error 13010 on a Mac / Wie ich den iTunes Fehler 13010 auf meinem Mac behob

After using Mac iTunes for almost 19 years trouble free i finally encountered the error 13010. iTunes refused to start and all the workarounds  posted over the internet including deleting the "genius.itdb" file did not work. Bad feeling when 20 gigs of music practically have vanished (yes i do have backups). I grabbed one of my backup drives, connected it to an old translucent G3 iBook and compared the content of the folder user/userX/Music//iTunes with the one of the corrupted machine. Seems like in the folder of the corrupted machine a new file had appeared that was lacking on the backup drive. It´s name is 

iTunesLibraryExtras.itdb

Deleting this file did the trick for me. iTunes started properly again. 

Recently (i don´t know if it´s causally linked to some internet acivity i did recently) the file reappeared but iTunes still works flawlessly. If you ever encounter error 13010 it is worth giving this attempt a shot.

A screenshot of the aforementioned folder:

The file mentioned is highlighted in reddish