Hmmm, I'm not sure but is the one song repeating? If so, you need to change your repeat option to OFF, you can do this on the top line of iTunes under "Controls".
If not, as a workaround, I would just click on the playlist, then "Edit">"Select All". Once all of the songs are selected, I would hit play and then they should all play for you. I know you shouldn't have to do this, but....