Very weird... That should not be happening in normal use. :/
Essentially, you only get that error if the IP that requested the Secret Link page is not the same IP that submits the form. This is to prevent people from saving the page and keeping a local copy of it to mess around with.
YOU HAX0R.
I'll look into this... if it ends up being a problem, I will remove this security feature... it's not really necessary after my second rewrite of the anti-OCR stuff.