I can't neither upload a new avatar nor delete the current one.

When I try the first thing I get this:

"File upload failed. Tried copying to "/var/atlas/pictures/avatars/6.jpg" from "null". Why is anyone's guess. Maybe the file was really, really big? Contact an administrator if you want it fixed."

The image I'm trying to upload is, by the way, a 500x500 px, png format, 559 kb file.