I have updated the system settings (there is more than one place avatars need to be enabled in the system
) and it should work now ("Famous Last Words" Vol. 7; pp345).
Maximum size is 80x80 pixels and 19.5kB size. The system will resize any image over 80x80 pixels if you upload one but will reject anything over 19.5kB in size.
Let me know if it works OK now.
Bob.