Problems downloading on mobile device

When people access my blog to download my pdf on a mobile device, they are able to fill out the form, but then receive an error message “unable to fetch desktop version.” Is there some sort of setting I have wrong, or something I can do to fix this?

The form can be found here: http://www.mattmckee.me/be-social-updated-ebook-free-download/ Don’t know how to recreate the error for you since I’m typing this on a PC.

http://wordpress.org/extend/plugins/email-before-download/