I don't know what happened, but I can no longer create an instance of the Session Drummer vst.  I get an error stating something is wrong.  (Don't have the specific wording at the moment...)
 
So I searched my SDD and HDD for Session Drummer.  All I can find is the dll for the vstplugin.  No standalone exe...
 
How can I reinstall SD3 (without screwing up my Sonar X3 install)?
 
Thanks
 

Maybe this will help.
 
https://www.cakewalk.com/Support/Knowledge-Base/2007013357/Session-Drummer-3-is-not-being-recognized-by-SONAR-X3
 
 

In deed, it did!  Thanks
 
(I had the  Microsoft Visual C++ Redistributable for Visual Studio 2012 Update 4 installed, and SD3 worked in the past.  But something happended and the c++ package needed to be repaired...)