Most often, this error occurs due to the settings of Internet Explorer.
To fix it, run the browser and disable the "the standalone mode". Off and restart your browser. If you have turned off, turn, and then turn off again with intermediate restarts the browser. In the end shutdown should help (helps 90% of cases).
If this not help You, then:
Make sure that you have the latest version of Adobe Flash Player
Go into the World of Warcraft folder and delete the Cache folder.
Check the settings of security, antivirus and firewall - maybe they block the connection game. The game uses TCP ports 1119, 3724, 4000, 6112-6115.
Some users were able to resolve this problem resetting the routing table.
To do this, follow these steps:
[spoiler=Reset the routing table.]
Warning! In the process of executing the internet connection will be broken!
Press the Start button->Cmd->Ok
write command Route -f When the command completes the Internet connection will be broken.
Press the Start button->Control Panel->Network Connections->Click right click on "Local Area Connection" and select "Repair".
You may need to restart your computer, if the Internet connection is not restored independently.
Clean the folder c:\windows\prefetch
Maybe You can solve this problem with simple reload the PC.
If this instruction does not help You, write your problem on the forum by the rules. In this topic write everything you did to solve the problem.