Form Won't Submit - Error Message says: "At least one required field is empty...."

Hello,

I have built a form in Acrobat PRO and I will be using tracking to collect responses once forms are submitted. I have distributed the forms - saved locally and sent with my own email client - and the recipients are able to fill in, but not submit their completed forms - they are getting an error message: "At least one required field is empty....", even though their are no required fields empty. 

The form has a few different types of fields (date, signature, dropdown, etc) that are required, two radio buttons that are not required, and a few check boxes and a lasrge text box that is not required. I have two buttons as well: A "Reset" button to reset the form (as people may need to submit the form more than once for themselves) and a "Submit" button to send the responses to the tracked file. 

My license is purchased through an Enterprise Agreement and I am suspicious that there is a security layer that is preventing my staff from being able to submit the form ... so aside from any other solutions, can anyone advise how I might check any of those security settings in Pro? my IT department says they are unable to provide program specific support. Many organizations similar to mine use PDF forms for the identical purpose and they are functional - this is making me crazy... help please?