My clients are unable to submit the form, they said the form freezes up on submit

I have a technical question- I sent a jot form to a client and they are unable to submit it back.  They said it froze when they hit submit and it never sent.  They've tried multiple times on different days.  I just tried to open my form and every time I click on it, it disappears.  

The form is actually showing up, but they have a problem submitting it. The form freezes up on submit. Did you embed the form to your website? If yes, please try using our iframe method: http://www.jotform.com/help/148-Getting-the-Form-iFrame-Code.

If the form is not embedded, please try using this link: http://www.jotform.us/form/52285373157156.

I have just tested the form and it's submitting fine.

Thanks