You have a plugin or a template that has an integration issue with adsmanager. we could connect on your website to fix that. But I will request a bronze subscription for that.

If you want to solve by yourself just check javascript conflict check javascript files loading etc..

Please send us per email link to this post, + url + ftp + admin account we will check and fix your website this week.

Yes we will check your issue this week

Just to share with any one,

the bug is due to another component/template/plugin, that add a alt attributes on image without a value or empty value.
I think there is for SEO.

The code is not correctly working (don't check if it's HTML or a HTML string in javascript.

Anyway we improve our code to avoid issue with this bad working third party code

You should edit helpers/image.php

and line 296 replace the line by this one:
html = '<li class="ui-state-default" id="li_img_'+file.id+'"><img src="'+name+'" align="top" border="0" />';