To fix “An asset error occured during your last session” problem in MagicArena, apply this.

• Open regedit.
• Navigate to HKEY_CURRENT_USER\Software\Wizards Of The Coast\MTGA.
• Find “HashFilesOnStartup_h572346022“.
• Set its value to “0” (Default is 1).
• Close regedit.
• Launch MagicArena.

That’s all 🙂