Error 404 instead of form

This is weird, and I cannot find anything on it with Google…
When accessing the page from a regular computer – all is good.
Accessing it on a mobile phone, I get an 404 error message displayed instead of the form.
I have checked all the below, based on what I have read on the web:
wp-foot is in place
wp-head is in place
There’s no field called “name” in the form
looks ok on a desktop
error 404 on a mobile

On this configuration. since this is a live site, I cannot turn off plugins, to determine which one might interfere.

Here’s the URL:
http://www.matomymedia.com/mobile-monetization-2/

Thanks for any advice.

http://wordpress.org/extend/plugins/contact-form-7/