Hey I finally managed to make it work !
I was following this Serato Troubleshooting article without any success.
However I was missing one point about the files : not deleting the .xml and .itl but just emptying the files and keeping them in the iTunes folder.
After doing that, I opened iTunes to an empty library. I tried to check and uncheck the "Share iTunes Library XML" box and it updated successfully the .xml file.
When I added the music files it got to break the xml again, that's when I understood some files in my library were damaging the itl causing the non creation of the XML file.
So I did it again and added progressively the music files I wanted and it is working fine now.
The only inconvenience is that you loose all your library organisation like the playlists or the historical data for each song like added date or number of plays.
Hopefully it will last !
Thanks for helping me !
Cheers
Charles