I know this has been posted before by Rachel, but I didn't have the same situation and still cannot get the background image to work.
url is http://www.broadwaysingers.org
I have tried uploading both a jpg and and png but it didn't make any difference.
The background is white, then when it uploads the image, the background square turns a slightly darker color but no image appears. I save, and there is no background image.
I have tried reloading the socrates theme, but no difference.