Error 12 WorkaroundSource
#1 - 2013/01/25 10:05:00 AMIf you're currently receiving an Error 12 when attempting to log into the Diablo III PTR client, here are a few quick steps that have been successful in helping some players bypass the issue:
Step 1: Close out the PTR client and open up the live Diablo III client.
Step 2: From the login screen, click on the Options menu and then on "Account."
Step 3: Select "Americas" from the Server Region Selection dropdown.
Step 4: Click "Apply" then click "Accept."
Step 5: Log in as normal. You should now be on Americas gameplay region.
Step 6: Create a new hero.
Step 7: Log out and switch your region back Europe or Asia. Log back in.
Step 8: Exit out of the live client.
Step 9: Reset your password. You can do so here.
Step 10: Load up the PTR client.
Step 11: You should now be able to log in without an Error 12.
This should ensure that a Diablo III PTR license is properly created for your Battle.net account. Please note that you may need to wait briefly after switching your gameplay region before you can successfully log in to the PTR client. (Please also note that these steps may not work for all players.)