I have some hi-res photos (about 3000x2000 pixels, from the 1st of December 2009, Bono with footballers in London) and cannot upload them. I guess I satisfy all the rules...
I just found out that our photo hosting provider has some server problems, which can cause websites to be very slow or unreachable, which can be the cause of this problem. Looking at the nature of your error I am quite certain that this is exactly the issue you are facing.
Really? That shouldn't happen! It works fine for many other people, hundreds of photos are being uploaded each month. Maybe it helps to try another internet browser? Google Chrome often works well for these kind of things. (and is the fastest browser anyway)
Currently the page is not even available, so it if doesn't work tomorrow I will manually upload the photos myself in your name