I have an older version of Toribash, v2.7, and I recently noticed the newer version on the website. I downloaded it but was unable to register it using my old registration key. Do I need a new key? What's happening here?

There are no registration keys anymore. After starting Toribash, you need to go to the login menu. Then you can use your character from v2.7

http://forum.toribash.com/showthread.php?t=15546

Ok thanks!

On the first time you click 'multi player' in the main menu, you'll be prompted to enter your forum username and password.

Please put your registration key in the the user control panel page.
(http://www.toribash.com/forum/usercp.php)