I don't think Battle.net likes my Internet Service Provider! What can I do?:

Battle.net is designed to work with any 32-bit TCP/IP connection, however your Internet Service Provider or network may use a firewall or proxy server that is configured to restrict the port that Battle.net needs to send and receive game data. Contact your ISP or network administrator and ask them to open Port 6112 to send and receive both UDP and TCP/IP packets.