You've reached the publishing limit, To publish more Media, please upgrade to Pro »

A user with a free site is getting You've reached the publishing limit, To publish more Media, please upgrade to Pro » every time they try to upload an image. They're only using 8% of their media quota. I can't find where in the pro sites settings to go to change the quota for the free site, nor do I even understand why we're getting this message when we don't seem to be at the quota anyways. Ideas?