sure the picture sizes were correct (800x400) and the file format is the right one?

Yep I'm sure the size is 800x400. Right before I got that error, I had successfully edited a submission and uploaded a new one. Tried logging out/back again and other browsers but no cigar :/

EDIT: Seems I can upload submissions again, but only two at a time then it's like an hour after I can upload again. Is this a new site feature or a bug?

Weird. My only suggestion is to disable any adblocks you have on.

My adblock was already disabled long before these errors. It is weird. I've been a member since emptees and this is the first time that ever happened to me. Was thinking of making a new account, got other glitches like not able to change password, email etc... Hope a staff member could have a look at this.

Not sure why you can't upload/post but as for passwords, yeah I don't think you can change passwords anymore and that's probably a bug.