Seas0nPass needs an update for the new 4.3 (8F455) software that was released on August 1st. An update is currently in the works, and we plan to have it available soon.
As always, it's a good idea to backup your SHSH blobs to ensure you can downgrade your AppleTV in the future (http://support.firecore.com/entries/359097)
Keep an eye on this space for updates.
Update 8/19: The new 4.3 compatible version of Seas0nPass is now available. http://blog.firecore.com/5180