Added image to my User card. Failed. Tried again. Told I can't cause card already exists. Went to +image card itself and tried upload, same error. However http://www.wagn.org/wagn/Joseph_Boyle+image still says card doesn't exist!
This was a caching issue. I'm not yet sure how, but wagn occasionally gets confused about whether a card exists because the cache (in memory) thinks one thing while the database knows another. In this case all the data was correct in the database but it was cached as missing.
Whenever there are "existential" issues like this, it's worth clearing the cache. You should have a link to do this in your Administrator Links card.