WP Listings giving page not found every time I add page or post

This is appended to the URL while the plugin is importing listings. Your permalink structure most likely has a trailing slash. Check your Settings -> Permalinks to make sure the trailing slash is not there and save changes. This will do 2 things, if it set incorrectly then it will update the permalinks and everything will work fine. If it is set correctly, saving the permalinks will have WordPress regenerate your permalinks and resolve the issue.

I think this is the problem im having. Are you talking about using a Custom Post type?

If you have a trailing slash in your permalinks then the query string will be appended to the end of the permalink which can cause issues.

This will be addressed in the next update with a tweak to the occurrence of the appended url param.