Bumping this as I am having the same problem, except I am an officer in the group, able to perform all officer functions except assign roles. Like the OP, all the role boxes are grayed out for me, too.
OP, was this resolved? Did you find a solution?
Anyone else have any ideas? I hate to reinstall if I don't have to... P.S. - using the newest Phoenix, altho have tried in Viewer 2, as well, and same problem. Thanks!