KhaosHammer's post in Wrong version detected. was marked as the answer
Uninstall the Mod and reinstall it won't help you.
SCS updated both ATS and ETS and TruckersMP isn't yet compatible with that new update.
You'll have to wait for the devs to update TMP as downgrade your game to an older version won't work.
Also, please read the announcement on top of the forum :
Additionally, here's how you can disable the Steam auto-updates :
KhaosHammer's post in cant play MP was marked as the answer
The devs are working on an update. It will be released as soon as possible.
Just be patient.
Also, please read the announcement on top of the forum before creating a topic :
KhaosHammer's post in Unsupported Game Version Detected Problem(184.108.40.206) was marked as the answer
You can't downgrade your game version at this moment.
SCS released a new update today and TruckersMP isn't updated yet to match this version. The only thing you can do is to wait for the devs to update TMP.
They are working on it, it can take between a few hours up to +/- 2 days, but don't forget that TMP staff have a life, a job, a family etc... outside of TMP.