I've just finished installing movable type, and am now following Douglas Bowman's instructions for setting up a nice photo gallery using Photon (as seen here).

I've been able to follow all the steps rather well after playing around for a while. However, when I rebuild the site, I get this error:


I double-checked all the values, links and everything else. I also noticed that I didn't have a category, so I created one and the error still appears. Any ideas?