Hi,
it is possible that user pressed Submit button twice. You can include this JavaScript snipped on the page with BizForm:
jQuery(document).ready(function() {
jQuery(".FormPanel input[type='submit'], .form-horizontal input[type='submit']").click(function() {
var $button = jQuery(this);
$button.click(function() { return false; });
$button.attr('onclick', 'return false;');
return true;
});
});
it should disable the Submit button after first click. jQuery library has to be included as well.