I finally heard from stopbadware.org and got the specific code that caused the block. It was our guestbook and I have deleted the page and all pages that referenced it. So all should be fine -- unless they find something else to bitch about.
Frankly I am still angry that they do not contact the website's creator BEFORE the block. Because I never use Google to find the site, I would never know about the block except from friends who know to contact me. Their system of protection is very flawed because most sites that I find blocked I do not visit and do not know who I should contact about problems. I just go elsewhere. So a site's innocent owner might go for weeks without knowing there is a problem.
Thanks, Kit and Elpis, for letting me know. I will try to google my own sites from time to time, but it is just one more thing to fiddle with.