I too get this problem, but I did some testing.
It seems to be the wordpress image/media up-loader I used the plugin nextGen Gallery and images upload with no problems at all.
pic.
So on my wordpres site i get this error out of the blue
http error.
Only when uploading new images and media files now all my media files are pretty small in size and just yesterday i was able to upload images
im running the latest version of wordpress
