Message Upload Failed / Challenge Solution Proof (Refresh Login)
These two errors both require you to refresh your login.
To refresh your login, go to your game settings and click the "Account" button. On the Account page, click "More" and then click the "Refresh Login" button. Re-Login with your account credentials again, and then restart your game.
If this still doesn't work (or you have the Message upload error), delete a few of your sent messages. You can do this by clicking your profile, clicking the mail icon at the bottom, and then opening the sent messages screen. After deleting a few messages, refresh your login and restart the game.