I'm having the same problem. On Tropical Island and have completed stage 2 (all 4 golden bananas). I go to the 3rd and click the character to accept the next quest and it tells me I haven't met the requirements. I can't find anything anywhere in the game (like I need x amount experience) that tells me what I still need to do to advance. In the past once you have all 4 banana's I could just go to the next character quest.