There's a typo in the afterburner Joomla 2.5 template version 1.6.0 (24-02-2012).
File: /html/module.php
Wrong code (line 39):<div class="module m<?php echo $mc_sfx; ?>">
Replace this line of code with the following to get the module class suffixes working again:<div class="module <?php echo $mc_sfx; ?>">
(remove the 'm')