problems with questionnaire

HI!

I'm using a Zoho creator questionnaire for a graduation project where people have to give feedback on and upload their training sessions for the Amsterdam marathon. However, some subjects complain about not being able to upload their training sessions. After filling out all the required field the 'please wait'-text appears but than nothing happens, I'm not receiving the sessions either. Could it have anything to do with the verificationcode?

The questionnaire can be found www.elkestaptelt.com and than second tab in the menu.

Any ideas? Thanks in advance!