JoomSEF 4 is a new generation of Joomla SEO component for generating SEF URLs and managing metadata.
Version 4 was developed to be compatible with latest Joomla CMS - version 1.6. Due to a different API, it is not backward compatible with Joomla 1.5 or older versions.
If you want to support JoomSEF 4 further development, please purchase a paid version.