solved my problem.  my playback was set to stop on a certain measure (i'd never used that function before so wasn't looking for it).  I must have inadvertently clicked it at some point.

This happens when you add measures.  The automatic setting is to stop at the number of measures originally selected when creating the document.  (The default, if I remember correctly, is 31 measures.)  As an automatic setting, this makes absolutely no sense.  Many of us start with the default number of measures, knowing that the additional measures will add as we go, or can be added in bulk under the Edit menu.  Then we try playback and it stops after a certain number of measures.  Only if we know about this automatic setting will we know to change it as we go.  The automatic setting should be to play to the end, which would save us all a lot of time and confusion.

Where can I find the setting that tells it to stop on a certain measure? My playback stops immediately and I'm trying to see if mine is set to stop on measure 1. The green arrow just sits there at the beginning of the first measure and doesn't move.

Never mind, I found it after clicking the Playback Settings icon on the Playback controls. It is set to stop at the end of the piece, not measure 1, so that's not the problem.

The culprit could be a text repeat with playback effect Stop on Pass 1.

Thanks for the thought. By text repeat, I take it you mean indications like D.C. and D.S. None of the scores I am trying to play back right now use a text repeat.