Sneaking a peek at the dev version are we?
You are using features that technically haven’t been released yet, so not everything has been tested fully yet.
Can you edit your /modules/ajaxnav/ajaxnav.php in the following way so I can see how things are failing? It won’t fix the problem (and will probably make it worse, but it will help me figure it out.)
Make sure the version number of your install is 1.20.1
Find: (around line 250)
$response = str_replace('http://'.$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF'] ,get_settings('siteurl'),$match[0]);
Replace With:
$response = $buffer;
Find:
if(!$response){ echo __('AJAX Page could not be loaded.','awp'); exit;}
Replace With:
if(!$response){ $response = __('AJAX Page could not be loaded.','awp');}