We no longer support our extensions under Joomla 1.5, 1.6, 1.7 or 2.5.
Support for Joomla 2.5 ended on December 31st, 2014. We continued to support our extensions under Joomla 2.5 until December 31st, 2015, but major new versions released from now on will no longer support Joomla 2.5. We will make older versions that do support Joomla 2.5 available until December 31st, 2016, but the old versions will no longer be enhanced with new features.
In 2016 our focus will be on migrating our extensions to use the Bootstrap CSS styles, which will simplify our CSS files and provide a better experience for both users and site builders. We also have Joomla 3.5 and 4.0 to think about, which, it appears, will once again break all our extensions.
We will do our best to help you if you have a problem with one of our extensions in an older version of Joomla, but our memory of Joomla prior to version 3.0 is fading and if you encounter a tricky problem, we will ask you to upgrade to a newer version of Joomla and the latest version of our product.
We recommend that you keep your site up to date with the latest version of Joomla. From time to time significant security issues emerge, and sites that are not updated are quickly attacked once details of the problem are published. In general you can assume that our extensions work on new minor releases of Joomla, but if your site is critical to your business you should have a test site that you can upgrade and check first.
There's a handy table of Joomla versions and support dates at http://docs.joomla.org/Joomla!_CMS_versions