I took the liberty of updating a few things in the plugin including what I think is causing this error. I'd be surprised if the plugin was actually doing anything for you previously, because it wasn't able to create the necessary MySQL tables. Hopefully this updated version will allow you to stop spam dead.
I really wanted to use it and the developer seems to have disappeared. If he ever comes back, I'll be happy to remove my link:
I've updated it a couple times for various things, so I just tacked another .2 onto the end of the version number.
I've fixed the MySQL table creation error by removing the deprecated TYPE option.
I've also fixed the DNS blacklist issues. The queries worked, but they would return false positives. I replaced zen.spamhaus.org with the two correct servers: sbl.spamhaus.org and xbl.spamhaus.org.
I also updated the gethostbyname logic to prevent false positives. It will only show the banned ip error if one of the proper DNS blacklist servers recognizes the IP address.
I don't have much time to maintain a plugin, but I did fix what wasn't working for me -- and what most people are complaining about on here. I cannot guarantee that I'll be able to fix any other issues as I seldom have time to visit the forums.