Somehow, perhaps through roll-backs in Sonar Platinum, Melodyne has disappeared as a RegionFX insert.  It is still available as a VST Effect, but I'm sure it used to be registered as a VST3 and now the VST3 category is empty and it used to be found under RegionFx.   VocalSync is the only thing that shows up under RegionFx.
 
I have a working and registered copy of the full melodyne studio package: the editor and the singletrack editor, and Sonar's CCC claims it has also installed melodyne essential, the version that ships with sonar.   
 
Can anyone point me to instructions for getting melodyne working again?  The manual just says "If you already own .... it will seamlessly integrate ..." but that doesn't seem to be true. 

This is how I did it.
 
Remove from the filesystem all melodyne folders. i.e. \Program Files\......\Melodyne
Remove from the registry (careful here) Melodyne keys
 
Reinstall menodyne from CCC or from (hidden) \ProgramData\Cakewalk\Command Center\Downloads
 
This worked for me.
Know what your doing here though or get a tech friend to help.

Tried to do exactly as you said, bitman, but it didn't seem to work ... thanks for the ideas.

Possibly a bit painful but open the Plugin manager, do a reset and rescan of you VST's, this worked for me.  Though it is important that the rescan completes, I had it fall over twice due to another problem with another Plug.

+1, if Melodyne runs stand alone, this should work.

If Melodyne needs to be reinstalled you actually need to get a copy from Celemony directly. They create personal registered copies you must download and install.