This version requires PHP 5.3, 5.4, 5.5 or 5.6. The rationale behind this is explained in our statement of mid-February 2013. It won't install on hosts running PHP 5.2 or earlier. PHP 5.3.4 or later is required, due to show-stopper bugs in earlier versions of PHP 5.3. Important note on reading PHP versions: PHP 5.3.20 is newer than 5.3.10 which is newer than 5.3.4. Moreover, PHP 5.4.0 is newer than PHP 5.3.4.
This version of our software can be installed on Joomla! 3.2.x, 3.3.x or 3.4.x release. It is not compatible with end-of-life Joomla! 2.5, 3.0 or 3.1 releases. If you are using them please upgrade to the latest Joomla! 3 release available from Joomla.org.