Frederic86, you need to delete all the old F1RL install in your Rfactor before you install the v2.00 version. This will include files in places such as:-
rfm
gamedata/vehicles
gamedata/sounds etc. etc.
This mod suffers more than most for servers running many different versions, so you will get errors when you do not have the same as the server. It does not help that when you install v2.00, all online F1RL servers will look like they are running v2.00, even if they are really running v1.41!