I think many of you will experience the same problem like i do. Thus, I felt i should post the quick fix here. However, if u see any better fix or hot fix on the internet please do let me know.

problem:

“When I am in the post editor, and click the insert gallery button, and then click the scroll down menu to choose a gallery, the scroll menu shows a loading circle forever.”

Fix (Only for people who put their WordPress in secondary directory) :

Go “wp-content>plugins>nextgen-gallery>admin>tinymce>window.php”

then look for:

<script type="text/javascript">
jQuery(document).ready(function(){ 
    jQuery("#gallerytag").nggAutocomplete( {
        type: 'gallery',domain: "<?php echo home_url('index.php', is_ssl() ? 'https' : 'http'); ?>"
    });
    jQuery("#albumtag").nggAutocomplete( {
        type: 'album',domain: "<?php echo home_url('index.php', is_ssl() ? 'https' : 'http'); ?>"
    });
    jQuery("#singlepictag").nggAutocomplete( {
        type: 'image',domain: "<?php echo home_url('index.php', is_ssl() ? 'https' : 'http'); ?>"
    });
});
</script>

Ok, now change the

<?php echo home_url('index.php', is_ssl() ? 'https' : 'http'); ?>

to your domain name, for example mine would be http://www.tinieyes.com or maybe http://tinieyes.com

Ok, refresh your web page after edition. The problem should be solved

Chill.