I've tried to get answers to this with no success thus far. I can open Melodyne as a standalone and import audio with no problem, all functions working. However, when I open in Sonar Pro, Melodyne opens but does not show any audio in its window, it's blank throughout. Yes, I have the cursor right in the middle of a track of audio and I've opened melodyne in the FX of that track but again, nothing shows. I've tried both the 32 and 64 bit melodyne. I've contacted melodyne and they seem to have no solution since it seems to be a Sonar issue. Has anyone had this happen and found a solution? Does anyone have any idea what's going on with this plugin? Any ideas. I'm still waiting to hear from Cakewalk support. 

You can use Melodyne in the FX rack using the transfer function in the plug-in but I would suggest trying it as a Region FX. Make sure the VST3 version of the plug-in is installed, then right-click on a clip and select Region FX > Melodyne > Create Region FX to load the clip into Melodyne.

Thanks scook. Still nothing when loaded in the FX rack. Checked in Artist and yes it's a VST 3. Did as you suggested using the Region FX above and IT WORKED! I wonder why it takes this method to open?

Because the VST takes advantage of ARA (Audio Random Access) which can only be utilised in SONAR by using it as a Region Fx

Melodyne does not work like a regular FX plug-in. The ARA implementation (Region RX) is the reason Cakewalk is in business with Celemony. Usually Melodyne needs to be the first plug-in in the FX chain. Region FX happen before Clip and Track FX bins.

Thanks again. Thank God for forums!

Another way to put it is: if you use Melodyne as a regular VST, it does not see any audio until you first run the DAW's audio engine to play the project through the clip or track covered by Melodyne. That is the nature of VST, and Melodyne can work that way in any DAW. But ARA is a real advance. With region FX / ARA, the effect can initiate scanning the covered audio region (clip, track, or selected area) without running the transport. So Melodyne can analyze and find notes without first running the audio engine.