This is a concert! Yoko Ishida will be performing, it is being held at a night club in Springfield (Jaxx is the name of the club) the flyer I have says a one day j-pop concert bash. so it is not the same as the event they held in December.
the link to it is http://www.afxakibafest.com
(copied straight from the flyer)
They will also be having another around Halloween with Salia and Psychic Lover (every Super Sentai fan should be Squee-ing at the uber awesome-ness of this, lol) this is also just a concert, but didn't seem to mind if people dressed up since it is a Halloween "bash" (i think me and my group will be at least wearing our Boukenger jackets.
Also want to add, if you haven't seen Yoko Ishida live in concert, she is really great. I saw her about two years ago and the concert was alot of fun.