It may be a license key issue.
 
I had such an issue last year where Melodyne would not work properly with Sonar any more. I emailed Celemony support and a day or so later they created a download for me which I could then install. No problems since.

Something similar happened to me a few updates ago, but it was easily fixed. After an update to Sonar, Drum Replacer and some other ARA effects stopped working, and I'd get the same error message you did when opening a project with instances of those effects. It's been a while, but IIRC, the system just needed a full VST re-scan. Regardless, search the forum for "missing ARA effects" or a similar wording, and you'll find the answer. I know this is where I found it....

Well, I did what Celemony suggested: complete uninstall/reinstall of Melodyne. Once done, I did a plugin rescan via Sonar's Plugin Manager. Voila! It's baaaaaaacck...
 
BTW, I put all of my VST3 .dll files into a single directory. I just couldn't get my head around why each plugin needs its own folder. Native Instruments only uses 2 folders; one for 32- and one for 64-bit.

Ricebug
Well, I did what Celemony suggested: complete uninstall/reinstall of Melodyne. Once done, I did a plugin rescan via Sonar's Plugin Manager. Voila! It's baaaaaaacck...
 
BTW, I put all of my VST3 .dll files into a single directory. I just couldn't get my head around why each plugin needs its own folder. Native Instruments only uses 2 folders; one for 32- and one for 64-bit.

You probably didn't even need to reinstall but why listen to me
 

chuckebaby
did you try a rescan/reset of your VST plug ins scanner ?

 
 

The Celemony tech told me to uninstall/reinstall. Must...obey...all...tech...support... (add zombie groans).

I'm so glad to read you fixed it. This was one of the more disturbing problems I've seen and I don't own editor.
 
Yet.