UnknownHostException: session.minecraft.net
Problem You can login to Minecraft but when you tryto connect to a multiplayer server, you get an error about session.minecraft.net that says:
Internal client error: java.net.UnknownHostException: session.minecraft.net
Sample image: http://img192.imageshack.us/img192/3708/srrorh.jpg
Also, when you try to ping session.minecraft.net, you won't get a response from it. You may see something like:
C:\Users\YourUserName>ping session.minecraft.net Ping request could not find host session.minecraft.net. Please check the name and try again.
Cause The session.minecraft.net domain is either down, or has changed and your existing DNS server still points to the wrong place.
Solution You can change the DNS server from your ISP's default one to a different one, and try again. Instructions on how to change your DNS server can be found at the page on DNS Addressing - How to Change in Windows 7