Aha!!! Finally figured out the problem. The install was taking so long, I didn't sit at the computer and monitor it before. When I returned, I found the Access Denied message. Well, today I sat thru it and Bingo!
I have BitDefender and to close it out before the install, I right clicked on the toolbar icon and selected Exit. Well, that didn't completely close the program...it was still protecting the registry. When it came time for the SP3 update to do the registry, a permission window for cmd.exe popped up and I had to physically allow access. When I did, SP3 installed perfectly. Apparently, on the previous install attempts the permission window popped up but I wasn't there so the BitDefender program did its job and denied access for me. Lesson learned; Either stay and physically monitor the install or manually turn off each individual protection in the security suite.
Thanks for all your help and maybe my experience will help someone else.
BTW, SP3 is working flawlessly on both computers.