Don't add a shield to your Demon Hunter's templar
It seems like it is the Demon Hunter's templar that causes Diablo 3 to crash. There are many reports about this bug in the Blizzard forum and also the site Eurogamer reports about it as well. Laurelin writes:
"Don't trade your equipped shield with the Templar, The game boots you out, and you can't log back until Blizzard notices and fixes this issue."
There has been no official word from Blizzard at this point, but there will probably be an update within a week or so when they fixed a couple of bugs.