Hey again,
Sorry for the double post, but my problem is now solved, thanks to AR »rex.racer for that.
Since I saw that some people had the same problem, here what you have to do :
- Delete the pack from you files (document/Maniaplanet/Pack/TmPlus.Gbx)
- Then go in the game, and delete the station that was holding the previous version of TmPlus
(1 clic on it, then press "del").
- Go for a clean installation on a free station. It will work this time.
So yeah, the old station was the problem.