I don't know when the problem started, perhaps with some updates of WordPress or Plugins.
The problem is that the Media Library only shows broken images icons. Also, when I want to set a featured image (either NextGen or normally) in a post, it only shows broken links icons (and images on the site/post).
However, when I upload an image into Nextgen Gallery, and insert it with the image tags, it works fine.
I've already 'downgraded' the Nextgen gallery some versions, but that does not seem to fix anything. It does not seem to be a browser problem either.
My theme is Videozone. the site is http://www.metal-exposure.com