It sounds like they've been added as an Admin at the team level, instead of being added as a member to the board themselves.
Being a member (or admin) of a team does not automatically grant access to a board, so a user will also need to be added to the board as a member.
Open a board and click on the "Show Menu" button in the top right-hand corner. The Add Member section is at the top. Once you are a member of the board, then you'll be able to work it in completely.
Here's some helpful guidance on how to add members to a board: http://help.trello.com/article/717-adding-people-to-a-board
And also a helpful guide on changing permissions: http://help.trello.com/article/791-changing-permissions-on-a-board
You’re invited to our first ever Trello User Groups Good news for current and aspiring Trello enthusiasts! We’re launching Trello User Groups so that you can network, share ideas, solve ...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG