Those errors appear to be coming from threads/posts that are in forums which you are requiring users to be logged in to be able to view them.
Since Google's crawler does not log in to sites it will give the "403 Error", meaning it does not have access to the information on the page. You should not be submitting any Forums/threads/posts to Google in which you require a user to be logged in to be able to view the information. All forums that require a log in to view should be entered into DBSEO - Sitemap Settings - Page Settings - Excluded Forums.