Installation Update Resolved
I finally got this problem resolved - I'm not sure what did it, but I deleted the wincache_dat file, rebooted my machine, did not open DW3 at all, then opened Extension Manager and removed the 2 extensions there. I was then able to install the upgraded versions of CSSMenuwriter and GoogleProMaps.
It wasn't without pain - but I'm finally back in business.
Thanks for your support, Ray!