Just did a whole entire clean reload of Windows 10 and Sonar X3e Studio.  Ugh.  Anyways, up and running now, but Sonar comes up with the error message showing that all of my MeldaProductions plugins are missing...  "They may be missing or improperly installed on your system."  I have downloaded and reinstalled the plugins as per Melda instructions. Don't understand why it doesn't see them. 
Here's the real confusing part: I can invoke a brand new instance of any of their plugins on my project, and it works fine. They come up on the VST scan as they should. But Sonar claims that any of the previous plugins that were put in my project(s) before the system reload are missing. 
Is this some sort of weird path issue?

Hi. This is just a guess. But did you install a newer version of Melda plugins when doing a clean install? Could it be that they do not have the same ID as the older versions? Other will know better.
All the best.

Zargg71
Hi. This is just a guess. But did you install a newer version of Melda plugins when doing a clean install? Could it be that they do not have the same ID as the older versions? Other will know better.
All the best.

I've gone to Melda for help, and they think it's a path issue, not an ID issue.....  weren't able to help other than that suggestion.  But I don't know where Sonar would be looking for the "old" plugins, other than where the new ones are installed.

Did you install Vst2 or Vst3? 

Zargg71
Did you install Vst2 or Vst3? 

they don't give you a choice...  VST3 only... and I asked about that, thought that was the problem, but apparently not....?  they have 3 different download versions to try, and I tried them all. 

I am not sure which installer you are using, the 10.03 installer on this page has options for VST, VST3 and AAX on the screen immediately after the license. Pretty sure 10.02 and 10.01 do too.

I agree with scook. I have had Melda plugins on my laptop for a few years, and seem to remember the option to install Vst2 or Vst3 (at least). 
Vst3 defaults to C:\Program Files\Common Files\VST3.
Vst2 defaults to C:\Program Files\Cakewalk\VstPlugins.
Hope it helps.

After clean install of Windows, MeldaProduction might not show "C:\Program Files\Cakewalk\VstPlugins" as the 64bit VST2 default path.

scook
After clean install of Windows, MeldaProduction might not show "C:\Program Files\Cakewalk\VstPlugins" as the 64bit VST2 default path.

Good point

OK, Scook,  that did it, thanks!   And yes, there is an option to choose VST, VST3 or AAX plugins on the download.
 
What grasshopper has learned is that although I chose both VST and VST3 plugins for my download, Sonar defaulted to only scan in the VST3 plugins. I had to go into the Plug-in Manager and specify the path to the VST2 plugins, force a rescan, and once that was done, all was good. 
 
Thanks guys!