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 2.5/3.0. Due to a different API, it is not backward compatible with Joomla 1.5 or older versions than 2.5.6.
If you want to support JoomSEF 4 in further development, please purchase a paid version.