This typically happens when the file browsers connector.php file does not have permission to be executable.
It results in the < Resource Type > not being set and files are not loaded in due to a 500 internal server error.
What to do
Joomla recommend 755 and 0644 for folders and files respectively with suPHP installed running on PHP & MySQL 5+ which gives us a level playing field to work too however, you may be using a different configuration and therefore may need to use 777 for your files?
The point being is that Joomla like our editor needs the folders and files to be read/ writable and the entry points for the browsers (this being the file which your browsers need execute) such as the connector.php file must be read/write and executable.
I would contact your hosting provider and ask them what the correct permission should be for your server.
To read Joomla!'s reply on this matter please see:-