Original Poster Update:
Before trying the above suggestions, I tried to import audio from a different session (at the same studio).
Of the three songs we recorded that day, I was able to import tracks from
one. Tracks from the other two songs behaved the same thing I described above - the progress bar below would say the program was converting, but at 100%, no clips would ultimately show up. I tried to import the problem clips into their own Sonar session AND into the session which allowed the one song. Same result - no sound clips materialized.
And once again, ALL the clips in question open without a hitch in Adobe Soundbooth CS4 and Windows Media Player.
So before I begin messing with Global Options and what not - why would one batch of tracks work just fine and the others not? That seems like relevant imformation ...?
Thanks everyone - I know you all have other things to do during the holidays. :)