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I added images to the server via CiviMail (KCFinder). But when trying to use the UI to insert an image and click "Browse Server" I receive an "Unknown Error". None of the images are displayed. I'm unable to locate the images and insert them into a new mailing. Already checked the Resource URL and Directories. See image attached. 
CiviCRM 4.7.11 and WordPress 4.6.1
You may want to check Firewall or the settings in WPSecurity (plugin) if you have that installed. I ran into this problem and it was an option in WPSecurity for "Bad Query Strings" which blocked access to thumbnails in KCFinder.
According to the plugin... Deny Bad Query Strings
This feature will write rules in your .htaccess file to prevent malicious string attacks on your site using XSS. NOTE: Some of these strings might be used for plugins or themes and hence this might break some functionality. You are therefore strongly advised to take a backup of your active .htaccess file before applying this feature.
Check the ownership of the folders where these images are uploaded to.
