Had to go into debug mode for this one and reactivate plugins 1 at a time.
Am using a Windows 2012, IE8 server. WordPress 3.5.1 - WordPress debug mode is providing this:
Notice: get_current_theme is deprecated since version 3.4! Use wp_get_theme() instead. in C:\WWWRoot\mywebsite\wp-includes\functions.php on line 2839
Fatal error: Call to undefined function wp_reset_vars() in C:\WWWRoot\mywebsite\wp-admin\user-edit.php on line 12
Since this will bring down the admin side of the site I have marked it as critical.