Just a guess but did you install that vst to the default folder?
I usually install everything to C:/Program Files/Cakewalk/Vstplugins but I have had a couple vst's that would only work if installed to the default.

I think that's your problem.  The plugin shows on the available plugin list, but not the file list on the right, correct? You have to highlight the plugin in the middle list and push the add button to move a copy to your default (or whichever) plugin file. Then use the move up or down buttons to position it where you want it.  
 
* And remember to save the file before closing the plugin manager!  The plugin should now show in the plugins file.

Yes, that would be the problem if one is not using the "Default All Plug-ins" layout. I asked  previously about the plug-in layout. SONAR by default displays all plug-ins; the layout is built on the fly and cannot be edited. On the other hand using any other layout requires plug-ins be manually added to the layout using the Plug-in manager layout editor (the right side of the Plug-in manager).

FuddyDuddy and scook:

I have done what you said, I have highlighted, and moved the plug-in to the right  and have saved the file in Plug-in Manager.  

When I load plug in manager, I can see the Plugin in the right column - where it is supposed to be.  The problem is
when I go to insert the synth into a project, it is no longer in the list.
 
MetalTek: I have the plugin not in the exact directory you mention - but in a directory where a majority of my plugins are.
Since it gets scanned by Plugin Manager and appears on my plugin list - I am assuming that is not the issue.
 
 
 

 

You may need to try a reset/rescan.
 

stevec
You may need to try a reset/rescan.

Suggested that. What seems really strange is the plug-in is seen enabled in the plug-in manager but is not visible when using the "Defaults All Plug-ins" layout setting in the menus and browser. Regardless of whatever custom layouts there are the "Defaults All Plug-ins" layout builds the plug-in list on the fly and should show every enabled DX and VST plug-in in the plug-in manager.

I appreciate all your suggestions.

One thing I am wondering - if it has anything to do with the plugin being properly authorized.  I did an online authorization and I got the message (on the Sonivox website) that the plug was "authorized."  I wonder if there was an issue authorizing it on my computer.  The reason I wonder, I took advantage of the freebie from the People at Addictive drums.  It was the Peavey ReVaulve VST Plug in and  I scanned it before authorizing it.   When I tried loading it, it was not visible.  After authorizing it, I did see it
in my list.  Maybe there's something similar going on.  I will investigate this angle and check with Sonivox support next week..

Thanks again for all the suggestions!