That happens sometimes with images that use some non-standard meta data. If that's the case you should see an error message in your browsers console as well that will detail it. The meta-data in question is added by some websites but does not appear on photos or images from Photoshop etc.
Hi Johnny, thank you for the reply. I solved the problem by going to my hosting Cpanel and putting all the limits of the php.ini to maximum. (sorry my bad english, i'm italian).
I hope this helps anyone who has this annoying problem.
Ah... yes that could also be a cause, thanks for sharing!
I've done that and still have the same error.
Giack

Hi, I have a problem when I upload some images. I get a blank pop-up that says OK !Can you help me?