I try to add other audio efx...for eg Vocal Strip. As soon as I do this I get a big "crack" in the speakers, the main outs go to full red peak and playback doesn't work. It usually requires Sonar to be exited, re-boot the audio interface to clear it all the re-load the project sans the insert efx. Why cannot insert (or even the main efx box on a track) be used on the same track with Melodyne?
 
Oh and it does NOT happen if there is no Melodyne in the track. I can insert as many clip and track efx as I like. I even altered the playback buffer to 1024 (from 256)
 
Thanks

In my experience: When you have done Melodyne edits, bounce to track. Do not leave active Melodyne in the Project. It's begging for troubles. Melodyne is heavy and complicated, and it needs (practically) uneffected sound to do the pitch reading.