Some users have been experiencing an 'Invalid Command Line' error when updating or installing the game. We released a fix for this issue in the December update, but unfortunately some users (primarily users with spaces in their %TEMP% paths) will see this error again in the January release. We expect this to the be the last release in which users experience this bug.
When you encounter that error, please take the following steps to resolve it:
- Download the latest installer from https://mtgarena.downloads.wizards.com/Live/Windows32/MTGAInstaller.exe
- Run MTGAInstaller.exe. It will update MTG Arena without causing the error.
If you continue to encounter any issues related to that error, uninstall and reinstall the game.