Wipe phone.
Remove the user from BES and wait a min then add back.
Try again.
Sometimes in the ITAdminque (in the BES database, dont go unless you know what you are doing)you will find the users id with no pin. Its like BIS plan almost activated but was stopped short. BUt some stuff remains in the BES that wont let it activate after changing to a BES plan. Removing the acct usually removes the ITAdminque entry after a min. Its like a punishment for getting BIS plan.