I feel so silly because no one else seems to be having this problem, but I can't get this plugin to work even right out of the box. I double-checked and its file path is fine (I saw a previous post about an extraneous folder but that's all fine).
Thinking it was something funny with my theme, I re-activated the default Twenty Eleven and it still didn't work. When I display the form with a shortcode on a page and try to submit, I get the error message defined in the settings (by default, "There was an error. Please ensure that you have added a title, some content, and that you have uploaded only images"). When I display it by hard-coding it into the page template and try to submit, I don't receive any message but a "submission-error=1" is tacked onto the end of the URL and I don't have any pending posts in the Admin area.
Does anyone have any ideas? This is extremely frustrating and I'm worried that I'll have trouble getting support in the future - seems like this awesome-sounding plugin has been all but abandoned.