Some synth plugins suddenly not available in the browser in plugins button, in Sonar X3b. Using plugin manager I made those synth plugins available in the browser window. But I found that those effected synth plugins would not load into a track.
 
I have been gradually reducing the number of plugins available and Sonar X3b gradually started to load the plugins affected. Plugins like Rob Papens Blade and Punch, Native Instrurments Massive, Korgs M-20. If I put all the plugins back the problem came back.
 
Another strange thing is the affected synths will load into an effects bin, but not the instrument track. In the browser using the synth button, pressing the synth + control I found that insert synth is blanked out.
 
If I go to Sonar X2a the plugins loads as normal, though Waves plugins not available as they were converted to VST3 format.
 
I have un-installed Sonar X3b and re-installed it, no change.
 
This all seemed to happen yesterday when I installed Waves Version 9.14 software update. But it might just be a coincidence. I also had a computer windows freeze.
 

I just posted about a very similar issue.  I'll check, but I think at least one synth is unavailable (Kontakt 5).
 
Sux that this is happening to you, but I'm glad it's not just me :  )
 
Let's hope someone and/or bakers can provide guidance.

Another thing is when I had the plugin count down around about 200. I saved a project with the affected plugins in it. When I put the plugins back to 735 and reloaded the project, the affected synths loaded with the project. But I still could not load any of the affected synths from the browser into the project.
 
The VST plugin management has been modified for Sonar X3, so its possible a few bugs have been introduced?.

I wonder what you mean when you say "made those synths available in the browser".

All plugins, synths and fx are available in the browser anyway.

Also Sonar doesn't convert plugins to VST3, but you can set it so that if you have both VST 2 and VST3 versions of the same plugin, Sonar will load only the VST 3 version and replace VST 2 with VST 3 versions in projects that were started with VST 2 of that same plugin.

mudgel
I wonder what you mean when you say "made those synths available in the browser".

All plugins, synths and fx are available in the browser anyway.

Some plugins disappeared  from the browser window and when using plugin manager made them available in the browser, they would not load in track view. They would load into an efects bin, which is strange.
"All plugins, synths and fx are available in the browser anyway." But not if some disappear. That if the problem.

mudgel
Also Sonar doesn't convert plugins to VST3, but you can set it so that if you have both VST 2 and VST3 versions of the same plugin, Sonar will load only the VST 3 version and replace VST 2 with VST 3 versions in projects that were started with VST 2 of that same plugin.

Sonar X3b did change all my Waves VST2 plugins to  VST3 automatically. I did not change Waves VST2 to VST3.

I have solved what the problem was, it was the installation of Waves 9.14. When Waves installed the new files it did not install over the previous version.
 
I uninstalled Wave 9.14 removed any Waves dll left and reinstalled.