Hey @iksen,
Solution 1:
"Usually it appears when you try to update the multiplayer launcher with the game open. First, check if ETS2 process is running. If so, end it and try again. If this doesn't help delete core_ets2mp.dll, re-open launcher and re-download file. Path: C:\ProgramData\TruckersMP"
Solution 2:
Press the Windows Key + R (Win+R) on your keyboard
Enter "%programdata%" and press Enter (without the quotes)
Find the folder "TruckersMP" and delete that folder.
Navigate to C:\Program Files\ and delete the folder named "TruckersMP Launcher"
Go to our website and re-download and install the Launcher with admin privileges
Open The Launcher with admin privileges and click "Install Available Updates"
Solution 3:
Download Ultrasurf.
Run Ultrasurf.
Open TruckersMP in Administrator Mode. Install the available updates (only the first run with Ultrasurf), wait for it to finish and Launch button appears.
Exit Ultrasurf
King Regards,
[GökBörü] "Berk"