What happened to the Media Manager?
From Joomla! Documentation
Revision as of 03:33, 31 July 2009 by Chris Davenport
With the release of 1.5.13 a new bug was introduced in the back end, a view is causing a problem for the Media Manager to load successfully. You can find the related tracker item including a patch here: [#17319 Media Manager is broken]
Official and tested patch, including patch instructions are available here