Board Thread:Questions and Answers/@comment-1362555-20140519102441/@comment-4936165-20140618193356

It turns out that Jason was fired from the show and has been gone since January. Seth agreed to take over during that time. This is information came from a person who went to visit the studio during a recording session.

"Also, Jason Biggs was kicked off the show, and has been replaced by Seth Green. I was heartbroken when I first heard the news. I really admired Jason... But then I thought maybe this was for the best, some of his tweets were really offensive to some people, so it makes a little sense now... Still I'm upset about it... "

Seth probably was not ready until season 3 and Dominic was filling in for him.

http://skyblue033.deviantart.com/journal/I-m-Back-You-Guys-426792681