Images not uploading properly on multisite

I have a multisite. One client has a site on my multisite mapped to the domain:

As you can see by looking at the front page, images are no longer visible on her site, even though images used to work.

I logged into her site as a regular user to test this. I uploaded an image. It showed up in the post with a box of the size of the actual photo, but just a blue question mark like the others. When I look at the media library, there are just a bunch of squares with blue question marks in them. But when I go to each individual image using the "edit image" link, I can see the images just fine.

I have searched around for a solution have found references saying that php scripts, etc, running on the main site of a multisite could cause this. ???

Any ideas for a solution?