My monthly scans have been running normally, but this one has given a message window about Bit Defender Threat Scanner problem. I could not clear this window, and it prevented me from fixing the scan's listed problems. Was able to close Spybot eventually by using Task Manager. When I opened Spybot again it did not recognise that I had run a scan. And I got another message: Runtime Error 216 at 3A9055AA.

No mention of Bit Defender in your FAQ's. Google search mentioned some instances, and suggested, for the Free Edition, a re-install of Spybot.
Should I also consider a re-install?