Can't switch characters in Free Play levels?

[Zanzibar Buck-Buck McFate]

So I've just beaten the Daily Bugle side mission. Now I want to replay in Free Play to get everything else. But when I start the mission, I get Coulson and Ock as usual, regardless of who I walk into the Bugle door with. When I hold Y to bring up the character select, nothing happens. And when I swich to two-player mode to try with holding U on the keyboard, nothing happens. What am I doing wrong??

[Zanzibar Buck-Buck McFate]

NVM, figured it out -- if you enter the building, it's in story mode. You have to do FreePlay mode from the helicarrier.