When I see threads like this I try the function out to see what happens, and try to get it to mess up. I haven't been able to, and I'm using it on my office computer with the most recent SONAR updates and Melodyne Essential.
Try this: insert any WAV file, then insert Melodyne under Region FX. Under Algorithm, change the default to Percussive. Now that you've set the default, you can remove the WAV file.
Also note that you can't drag anything other than a standard WAV file to the timeline - no groove clips, REX, etc.