Media manager not opening in popup/overlay (front end)

On my current site, I have the wpmudev plugin ‘directory’ installed – which allows you to upload a featured image from the front end on a designated page.

Clicking ‘set featured image’ should open up the wp media manager popup and allow you to add a featured image, and when selecting the image, it would close the popup and my image would be set.

My issue is that when i click on ‘set featured image’ – instead of the overlay/popup, I get directed to a page (url extension) wp-admin/media-upload.php?post_id=4362&type=image&TB_iframe=1 which lets you select an image, but doesn’t allow you to set it, or return back to the original page.

Has anyone seen this issue before? I’ve changed themes, uninstalled all plugins, tested on all browsers, all networks, created a new user etc with all kinds of permissions to no avail.

Any help greatly appreciated! The guys at wpmudev can’t seem to help either.