iPod shuffle not adding/deleting music on Mac

Still use my shuffle on bike rides but now when I hook it up to my MAC I cannot delete or add music. It will show what is loaded, also show Albums, Artists, etc. but it is all translucent and you cannot make any changes.

Help! Is it a problem with the shuffle or the MAC? MAC is approx. 1 year old. Have 2 shuffles, same issue on both.