Hi, I had this problem.
Make sure you are opted into the public beta on steam to do so you need to go to steam, library, then right click on ETS 2 --> Properties --> Betas --> Select 1.24.
This will now download if you are not on this beta please give it time,
If it installs i recommend that you restart your PC.
Launch ETS MP in admin mode, click play.
Now it may say that is has crashed. do not panic this happend to me, it just takes some time to start up and load, wait a max of 5 mins and it should load within that time. if not message me back and ill offer more assistance