Well I finally got back to testing out PHD again...
... and it works.
I upgraded to ASCOM v5.5 from v5.0. I haven't changed anything else, and voila!
Gotta be happy with that.
Unfortunately, I had problems with my GPS and other little technical gremlins tonight, so it was productive in terms of images or spectra, but at least I should be able to start guiding now.
Al.