Ken, This is an odd one. There isn't a preference that allows this. So these things come to mind (assuming that you are playing from the Library in the left column):
a) Shuffle feature is on
b) Every other song is unchecked
c) Error in ripping the song and the song length is 0:00 (how I have no idea)
d) the album you are listening to has guest artists and the sorting by Artist is not including those songs with guest artist (coincidentally at every other song)--usually syntax is Artist name feat. xxxx
