Sisterhood of the Traveling Pants 2
Allegedly, Amber Tamblyn, America Ferrera, Blake Lively and Alexis Bledel signed on to the original movie and there was a clause that committed them to do a sequel. No one expected the original movie to become a cult hit and make as much money as it did. Then America Ferrera hit the big time with Ugly Betty and won a bunch of awards and the studios decided to cash in. Of course it didn't hurt that Blake Lively became a pop culture sensation on Gossip Girl. Supposedly several of the stars didn't want to do the sequel but their original contract forced them to.