Thanks scook.  I used your link (couldn't remember where to find that!) and followed those instructions.  It let me use one of my other SNs and seemed to load fine.  There was no stand-alone version so opened SPLAT and tried to load it but got the same dialogue box.  Again, none of the RCs worked including the one associated with that SN.
 

The default location for stand alone version is "C:\Program Files\Cakewalk\Vstplugins\Dimension Pro"
I do not recall a version since at least since X1 that did not have the 64bit stand alone in that folder.
I always used the stand alone before using the Command Center. Still running SONAR as administrator would probably work too.

Success!  Yes, I ran the standalone DP executable from that location as administrator.  The registration dialogue came up but this time it accepted the correct RC.  It now loads fine in SPLAT.  It did not change the CCC listing which still shows a different SN.
 
Thanks so much scook!

Works for me. I went to "C:\Program Files\Cakewalk\Vstplugins\Dimension Pro" clicked on "Dimension Pro x64" and selected run as administrater.