Had similar problem but i couldnt even see my media in the gallery, much less edit. The problem was a plug-in (as usual) as MacManX (Sir James Huff) had mentioned. The plug-in I had the problem was:
Remove Query Strings from Static Resources
Remove query strings from static resources like CSS & JS files. This plugin will improve your scores in services like PageSpeed, YSlow, Pingdoom and GTmetrix.
Version 1.0 | By Your WP Expert
Thanks
