I am looking at using this plugin but haven't tried it yet, so this is just a suggestion, but the plugin description says:
"Ad limitations by author, category, tag, page type, and much more"
So until you get a response from the developer I'd suggest trying this
- Go into your categories one-by-one, and make sure they each have a good, descriptive & totally unique keyword / meta tag / meta description associated with each of them, or maybe in your case use the category names etc for all the meta tags (... one suggestion here is to install the free plugin, "SEO Ultimate" available from this site - it's fairly new but very good & it allows you to control all the meta tags, descriptions, keywords etc - plus you can do it quickly & thoroughly because they are listed on the one page within SEO Ultimate plugin.... highly recommended).
I think by doing it that way you are giving the banner plugin a better way to associate the banners with a particular word/term.....
Hopefully that should help - let me know