I'm trying to edit a harmony track using Melodyne  - when I right click the clip in this particular track's take lane and select Region Fx-> Melodyne->Create Region Fx, it acts like it's going to load, then nothing happens.  Under Edit, the last Undo step is whatever I did PRIOR to trying to create the Melodyne fx to edit, so it never happened.
 
In other tracks and other take lanes within this track, Melodyne is still loading OK, so this is something specific to this take lane.  I had just edited the first clip in this take lane with Melodyne, then bounced it to clip - and now none of them in this take lane will load.  (And I already saved the project, so the undo steps are gone.)  I already tried shutting down and re-loading, didn't correct this problem.
 
Anything I might have reset that's take lane-related that would have caused this?

Not sure why this occurred, but I found a solution, in case anyone else runs into this.  I bounced the offending clip(s) (bounce to clip), and then it will create a Region Fx.  This had to be done on a clip-by-clip basis, fixing one did not fix the entire take lane.  Not the path I'd prefer to use to correct it, as I had some clip envelopes (pan, gain) I didn't really want to make permanent yet - but it allowed use of pitch correction with Melodyne.

The clip envelops were the problem. Region FX clips do not support clip envelops. See http://www.cakewalk.com/Documentation?product=SONAR%20X3&language=3&help=Region_FX.01.html for other Region FX clip restrictions.

Other clips were working with clip envelopes on them...  My understanding is that Region Fx doesn't support clip envelopes, but it doesn't prevent it from working.  I had tried deleting the envelopes, and that still didn't resolve the problem.  So it doesn't seem to be solely related to the clip envelopes.