Urgent Help Needed- Clips lost "connection" to audio file

I've been working with Sonar since version 1 and this is new for me:  after mixing down a stereo version of my song (or perhaps after freezing tracks), several clips do not "contain" audio data any more.  If I right click on the clip and choose "Associated Audio File", I can see the audio file it should be referencing...and in fact the audio file exists in the audio folder!  Somehow the "connection" or reference to it is lost.  The clip itself shows as having no wave form.
 
I am at the end of a very long term project and this was literally my final mix of this song which needs to go to mastering ASAP.  When I listened back to the final mix one last time, I noticed that the guitar solo was missing in its entirety (the track and all effects/automation/etc are there, but the waveform drawing on the clip shows nothing and the output from the track is nothing).  I went back into the file and saw that the frozen track had no waveform, so I unfroze it.  About 75% of the clips "came back" after unfreezing, but the other 25% still show no wavewaform/have no audio.  Again, the associated audio files are in the audio folder...
 
Any ideas what could be happening?  These clips were not "bounced to clip".  They still show the original clip name  on the clip header from the time they were originally recorded.
 
Any and all help is greatly appreciated.
 
Thanks in advance!
 
Sol