I just installed Sonar Platinum and tried to test Melodyne but when I did it froze Sonar and I couldn't do anything until I hard reboot my PC. I couldn't even kill Sonar using task manager?
 
Has anyone else had this problem?
 
This is what I did:
 
1.) Recorded 10 seconds of audio
2.) Highlighted the audio and added Melodyne to the clip
3.) As soon as I did that, Sonar froze and I could do anything.
4.) Reboot and tried again... same result?
 
This is a clean install of Windows 7 64 bit. Any suggestions?

I track with a buffer size of 64 and I'd often get Melodyne errors stating I'd need to increase my buffer size to 1024, and other times it would simply crash.  (The Cakewalk "Send Error" reports never seem to work, unfortunately.)  Sometimes even changing the buffer settings wouldn't work so well, so in those cases I'd bypass the RegionFX route and instead insert Melodyne as a plugin and transfer/capture the audio in real time the old fashioned way.  Sometimes this would work.
 
But I'm with you, because I just got a crash opening up a project I've been working on, which led me to do a Google search, which led me to this particular thread!  I'd been working on the project without any issues for the past few days, and for whatever reason, when I try to open the project today, it keeps crashing stating that Melodyne is the culprit.  That's kinda crappy.

Yep, crashes with Melodyne the culprit as well. Have uploaded a dump file which was apparently sent on to Celemony and yes, my crash reports from the window that sometimes jumps up has never been successful in Plt in sending on the reports...works in X3 though - haven't had to do that for a while with it mind you.
 
Yes, the buffer suggestions doesn't seem to work either. I've had Sonar Support actually confirm the 1024 buffer size is correct in X3 at the time and Melodyne still insisted it was wrong and to set it to 1024.
 
I agree with streckfus, try using it as a plug-in, and give the RegionFX a miss. If it's causing instability, only transfer a small section you want to work on and then mix down when happy...workarounds I know and not the most ideal way to use a plug-in. 

Just for the record (information from Noel) even though Melodyne throws up that error, if your buffers were adequate for what you were doing in Sonar, then they should be fine for Melodyne.

DJ Darkside
2.) Highlighted the audio and added Melodyne to the clip

Does this mean that you added Melodyne as a clip FX? Or did you create a Region FX?

Melodyne is not best employed as a clip FX or track FX. Due to the underlying ARA, it is best used as a "Region FX" which essentially passes audio from SONAR to Melodyne. It is also best used in small chunks (highlight a phrase or so, right click "Region FX->Melodyne->Create Region FX"). After edits, is best to commit to changes and bounce that region (you can always edit a second time if desired later). Multiple Region FX are undue overhead (and if not bounced the edits are actually saved in the project file which increases its (cwp) size substantially).
 
Edit: I noticed in your other thread that you are coming from X2 to Platinum. ARA support was first introduced with X3, so be sure to take a look at that and use Region FX when using Melodyne (which takes advantage of ARA).