Previously I advised against setting up your wordpress permalink structure to start with /%postname%/ as the plugin will not work with search engine friendly URLs turned on when your permalink structure starts with /%postname%/. ( WordPress Permalinks and AWPCP ) This is a known wordpress issue as WordPress themselves advise against setting up your custom permalinks to start with /%postname%/ due to potential problems with rewrite rules.
As it turns out, Another WordPress Classifieds Plugin will also not work in search engine friendly URLs mode if your wordpress custom permalink structure starts with /%category%/. Custom structures starting with values that are not numerical appear to prevent the rewrite rules from being executed and result in behavior ranging from getting 404 page not found errors, or being unable to load any page when you click the classifieds menu links.
I will continue to try to find solutions for these permalink/search engine friendly url conflicts; however, solutions will not be found immediately, so if you are using the plugin and modifying your wordpress permalink structure to include month, year or day value as the starting value is an option, please modify the permalink structure. If modifying your wordpress permalink structure is not an option, you will need to deactivate search engine friendly URLs in Another WordPress Classifieds Plugin.