I'm not sure if the lemm.ee interface is the same but when I go to my profile settings page there's actually two Save buttons, I was hitting the one at the bottom rather than the one in the middle of the page and that was tripping me up. Just a guess though, I didn't have to downscale the images or anything.
Not an error I've seen, maybe try clearing cookies or switching between cell and wifi if you're on mobile. Using a VPN? Uploading a standard jpg or png file, edited in a normal program? If you're using anything stranger than GIMP to resize it maybe it's a malformed image file. Other than that I've got no troubleshooting ideas right off, let us know how it turns out though