SeasOnPasson 4.3 (8F455)

I have a ATV2 with 4.3 (8F455) on it and I want to JB it.  I thought since the iOS is already on it, I don’t have to update the iOS.  When I start SeasOnPass and right click on the Create IPSW button, then select the 4.3 (8F455), it says not eligible for this version.  What am I doing wrong?

It said not eligible because apple is not signing the firmware 4.3 anymore. Please go to this page