Any number of issues can interfere with a form submission.
What browsers are the couple of users using? Maybe even OS?
What actually happens when they belt the submit button?
They could have enhanced security settings, especially in IE.
Alternatively it could be you and Dreamweaver and they have a browser that reacts to your work...
Browser compatibility is a broad brush, have you checked for IE10 in both win7 and win8...
This may be a long shot but anything is possible... I cannot submit to some forums due to some plug-ins installed in my browser. The site wants to interact with my computer in ways I am trying to stop hence they will not accept my form submission.
Have you asked the Dreamweaver forum if anyone has a similar problem?
Communicating with the couple of users and extracting information from them to pin point the problem is the best way to solve the problem. Pick your questions carefully as users can put the shields up quickly if they are treated as dopey.