HTTP Error loading to Media Directory

Hello -

I have successfully loaded two images which I am currently using in my Home Page Revolution slider. (The image of a computer, and the image of childrens' silhouettes under a night sky)

The focus of both of these images is a bit too high, so I used Photoshop to crop off the top of them, but when I tried to load these modified versions to my media browser I get an HTTP error.

Any ideas on how to overcome this HTTP error or why these files are failing?

thanks