Users receiving One Entry Allowed Error, 1st response

Users of our commencement form are reporting receiving an error saying they've already submitted the form, but they have not. This causes confusion and panic phone calls. How do we fix this problem? 

Unique Submissions feature is enabled in your form. 

How to Set Unique Submissions on a Form

It is set to Check cookies and IP. 

If your users are submitting the form from the same device or from the same IP address, I would suggest you to disable this feature. Set it to No Check.

You can instead use Unique Question feature if you want to prevent your users to submit the form multiple times. 

How to set Form Limits Based on a Unique Question