I just did a new install of version 2.1.0 and while checking my logs I noticed an entry in the 404 log as follows.
Text Formatted Code
Thu 15 Jan 2015 04:51:09 PM MST - 404 Error generated by 2@70.241.64.239 for url: http://www.mysite.net/layout/professional/jquery_ui/images/ui-anim_basic_16x16.gif - Referring url: http://www.mysite.net/admin/configuration.php
It appears that there is a file missing in the install download. It is included in the version 2.0.0 so I just copied it from there.