Right now I am ignoring ajax calls which allows spammers to register and leave comments with plugins that use ajax. admin-ajax.php is used for almost everything and not just logging in and comments. I can’t let Stop Spammers interfere with things that are not related to spam.
If I remove the line, then the page may not render for some people, instead the captcha screen would show.
I made the decision that I could not support non standard methods for logging in or leaving comments. The plugin will only work on plain vanilla websites. Any other way means that I have to code exceptions for hundreds of plugins. It is up to a plugin author to make his code work with Stop Spammers, and not up to me to support hundreds of plugins.
You should try commenting out the admin-ajax line and see how your site renders. Add a line to the deny list to keep yourself out, delete the cache, logoff and try browsing the site. If the page renders correctly and the site still blocks you from leaving a comment, then leave it that way. If the plugin blocks spammers and lets normal people through, let me know.
Remember, I make no money from Stop Spammers. I wrote it for my personal needs, but I am happy that other people find it useful. I will not be updating it unless I find something seriously wrong with it. There are hundreds of anti spam plugins out there. One of them has to be better than my plugin.
Keith