If you are having problems with Ajax in the admin menu of JReviews. Try this fix and see if it fixes your issue.

Go to this file
/components/com_s2framework/s2framework/dispatcher.php

Add this code

if($_REQUEST['xajax']==1) return true; // Fix for SERVER loss of HTTP_X_REQUESTED_WITH key

Before the change:

/**
* Detects jQuery ajax request
*
*/
function isAjax()
{
return (isset($_SERVER['HTTP_X_REQUESTED_WITH']) &&
($_SERVER['HTTP_X_REQUESTED_WITH'] == ‘XMLHttpRequest’));
}

After the change:

    /**
    * Detects jQuery ajax request
    * 
    */
    function isAjax()
    {           
        if($_REQUEST['xajax']==1) return true; // Fix for SERVER loss of HTTP_X_REQUESTED_WITH key
        return (isset($_SERVER['HTTP_X_REQUESTED_WITH']) &&
        ($_SERVER['HTTP_X_REQUESTED_WITH'] == 'XMLHttpRequest'));
    }

[Update]

Had another issue so this is another fix to try. Same file as before:

Old Code:

if($_REQUEST['xajax']==1) return true; // Fix for SERVER loss of HTTP_X_REQUESTED_WITH key

New Code:

if(isset($_REQUEST['ajax']) && $_REQUEST['xajax']==1) return true; // Fix for SERVER loss of HTTP_X_REQUESTED_WITH key

Old Code:

$xajax = new xajax('index2.php?option='.S2Paths::get('jreviews','S2_CMSCOMP').'&task=xajax&no_html=1');

New Code:

$xajax = new xajax('index.php?option='.S2Paths::get('jreviews','S2_CMSCOMP').'&task=xajax&format=raw&tmpl=component');