It may be a little late, but I experienced the same issue with my blog and discovered it was due to an interference between the AIO plugin and my theme. The AIO plugin seems to want to be the only one “subscribed” to the ob handler. To resolve the issue I commented out, or you can remove it if you wish, the ob_start() function call from my theme, and viola, the AIO plugin now works.
To figure out if you have the same issue, search your entire theme folder for “ob_start”. You can expect to find something like:
<?php ob_start(); ?>. If you see this, remove it, or to keep things simple just comment it out, as such: <?php // ob_start(); ?>.
You can see it in action at my personal blog
