The Battle.net desktop app is trying to connect to an invalid or nonexistent server.
Troubleshooting the error message "The code you entered cannot be claimed."
How to resolve mistakes claiming a CoD key on the wrong Battle.net account.
How to solve this problem on an incomplete Battle.net account
Troubleshooting steps for latency problems in Diablo III
Troubleshooting problems with the Battle.net friends list
Troubleshooting step for connection-related problems on Windows.
Troubleshooting steps for communication and transmission errors.
What to do if you have trouble with the captcha
The Blizzard Update Agent could not install in the specified folder location.