New Clip+ won't "Play All"

I’ve searched the forums and didn’t find this issue.  I just gave my 2 kids Sansa Clip+s for Christmas.  I am using a MacBook to drop songs onto the Music file on the players in the finder window.  One of them (I didn’t check the other one yet) will not “Play All” or play songs when attempted through the “Artists” list; the player just flies through the list of songs without playing a note.  I can play songs through the Albums lists or if I choose one individually so I know they loaded on the player OK.

And while I’m asking–how do I delete songs from the player using a Mac?