Cant' Delete Contacts from a List

I can no longer delete a contact from a group. When I select and contact and press delete, nothing happens (other than the sound made when I press a key and nothing happens).

A brief (meaning it only works once or twice per iteration) is to quit Address Book, and then I restart holding down SHIFT. That fixes the issue briefly, but after deleting 1 or 2 contacts, the problem reappears.

(note: a different issue also happens when trying to drag contacts to a list/group. I can do it one or twice, then it does not allow it. As above, I can reset things by quitting the application and restarting while holding SHIFT).

Help!!