[Plugin: Contact Form 7] Validation error with file attachment

When I try to attach a file, the form does not go through. I get “Validation errors occurred. Please confirm the fields and submit it again.”
When this happens, a white box shows up over the attachment field, but there is no text in it. I’m not sure if there is supposed to be or what. When I mouse over the box, it disappears. It looks like there should be some kind of message in it telling what’s wrong, but I don’t know.

Form is at this link:
https://www.stopthebleeding-il.org/meet-the-kids/your-story/

Thanks for any help!