Uploaded images appear as links


Images uploaded to the media library are appearing as links. The following error message appears when the link is edited:

Edit Image
Image data does not exist. Please re-upload the image.

It is a WP Multisite installation. Image uploading is working normally for the subsites but not for the main site.

When a downloaded image is added to a post, the html appears like this:

<img src="" alt="2015+NHL+Draft+Portraits+g1jF6WAnKNul" class="aligncenter size-large wp-image-262335" />

Normally it should appear like this:

<img class="aligncenter size-full wp-image-nsm-5-1392" src="http://allhabs.net/wp-content/uploads/sites/5/2015/06/2015-NHL-Draft-Portraits-g1jF6WAnKNul.jpg" alt="" width="600" height="400" />

No changes/updates were made at the site level between the time image loading was working and not.

I would appreciate your help with restoring image loading capability to the site. Thank you.