Since upgrading to 2016.3 (sonar platinum) melodyne (4.x editor) is only allowing one effects region per track... if I edit one section of, let's say a vocal track, and the try and create another region without bouncing the clip, sonar crashes and needs to be restarted .. I can create a region on another track ( but only one) . Also, the effects region seems to play both the new edited melodyne region as well as the original untouched track... creating a weird chorused/doubled vocal... anyone else getting this?

Hi, and sorry if this is obvious. But what are your latency setting? Celemony suggests at least a 1024 buffer. I have seldom needed to change it myself, but it could be worth a try, if not already done.
All the best.

Have tried all the way to 2048... no change :(

FWIW, I'm not seeing that problem with 2016.3 and Melodyne Studio 4.

I had the same issue with crashing in a recent project - the clip had to be bounced before another region could be created. Buffer settings made no difference here either - I didn't experience the chorus / doubletrack effect though..

I can get it to crash every time, with a "real" project.
...
Was tracking the issues, main concern was older Sonar projects. Pinged Celemony and was assured;
- "We paid attention to backwards compatibility"
- 64 bit "is even recommended"
- "ARA currently does not allow multitrack editing." ....
 
Ran a test project to check the reported issues.
- Open a project with a clip edited in V2 Editor = OK
- Open a project with a clip containing an active RFX = OK
- Add RFX to two clips in the same track = OK
-> was able to switch between the clips by clicking on the clip in the take lane. Melodyne would display the selected clip in the edit window
- recorded a 2nd take
!! Sonar crashed the first time I tried to add a RFX to the new take
Tried various combinations, was able to crash it one more time, but not repeatedly
Project currently saved and viable with 4 active instances of Melodyne RFX
- on both the same track and different tracks
- on both the same take lane and different take lanes
 
OK, maybe just a few upgrade wrinkles to be wrung out...?
 
Opened a "real" project.
!! Sonar crashes every single time I try to open any clip in a target track containing multiple vocal takes and two flattened comp takes
- No active RFX on any clip
- Checked take lane Mute vs Solo with > 1 active clip
-> still crashes
- Checked comp track vs. original take
-> still crashes
- Checked to make sure only one active clip in track (disabled all comp clips)
-> still crashes
- Tried deleting all but one comp take lane, split clip
-> still crashes
- Bounced all flattened comp clips 
-> successfully added V4 Studio as RFX
- Split bounced clip
-> successfully added V4 Studio as RFX to first small clip
-> successfully added V4 Studio as RFX to remaining large clip (1st still active)
-> was able to switch back and forth and edit either clip
 
My window for further investigation is closed for now. 
- I was not able to repeatedly reproduce the error in a new project with the OP's use case. 
- It appears to be track/take lane related atm as I'm able to add successfully add and edit V4 Studio as RFX to other tracks in the same project that crashes.
- Bouncing clips does something that helps. 
 
** Perhaps take lanes are considered to be "multitrack editing" which is not currently supported under ARA...?
 
<specs for test platform>
Sonar Pt 2016.03 / Melodyne 4 Studio 4.0.4.001 vst3 x64 / Win10 fully updated / x64 / i5820k / 32GB

Sound like you need to join us here. There is safety in numbers?
http://forum.cakewalk.com...Platinum-m3371621.aspx
 

More like misery loves company but agree there's benefit in shared experience. My issues are with 4 Studio, not Essential, but will toss my 2 cents into the other thread.