Intermittent Sending?

Has anyone found that forms are not always sent at all? When I have been testing my own forms they send fine but I’ve had 4 or 5 people saying they filled the form in and I never received their forms. I have received forms from some users but not the 4 or 5 I mentioned.

Any idea what could cause the problem?

I’m using the form to evaluate my college project and you can find it below

http://www.rossco-designs.com/RD-evaluation.html

Thanks