Form Alert Says I'm Over Disk Quota But I Don't Think I Am

I have submissions coming in via a form.  On one of the forms that was emailed, a message reads "Your account is currently over disk quota. Form submissions can not be added to your Form Manager...All future form submissions for this form will be sent to this email address until you are under disk quota. Delete any unwanted or unused files or purchase additional disk space by logging in to your account."

Well, I logged into my account, and it shows that I haven't even used half of my disk space, so I'm confused.  Is there a separate quota for form data?!