Warning! Please do not trade your equipped shield with the Templar follower in Act 1 of the Diablo 3 Campaign. This action causes a game breaking glitch called “ERROR 3006”! Be especially weary if you’re playing as the Demon Hunter class. As a result of this Diablo 3 bug people are reporting they get kicked out of the game and can no longer log back into Battle.net.
Blizzard has stated on their forums that they are looking into the issue and has advised players to stay away from the Templar while the company works to release a hotfix.
You can see the Diablo 3 Shield Glitch breaking the game in this video.