SPYBOT Home Edition 2.7 (licensed), Windows 10 - all up-to-date.

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?

Is it the Bitdefender Threat Scanner.dmp message shown on this page?:
https://www.safer-networking.org/faq...t-scanner-dmp/
If so, the page is saying to download Spybot 2.7. Since I see you already have that version of Spybot, then it is probably best if you get help from Spybot support.
You can use the contact form here. :)
https://www.safer-networking.org/support/#contactform