Bynes, 29, first made her name in the '90s sketch comedy series, before going on to star in her own Nickelodeon show, "The Amanda Show", a few years later, reported TMZ.
Next month, TeenNick will host Amanda's former co-stars Kenan Thompson and Kel Mitchell, Danny Tamberelli, Lori Beth Denberg and Josh Server for a special show celebrating the hit show.
The actress wasn't invited to the reunion, and only found out about it when a trailer was released online, claim sources close to the star.
"All That" aired on TeenNick for 11 seasons, from 1994-2005, and launched the career of a number of performers, who went on to star in their own shows.
Nickelodeon alum include Kenan and Kel, Mariah Carey's ex Nick Cannon, and Britney Spears' sister, Jamie Lynn-Spears, who starred in Zoey 101.