I sometime got a 401 error while loading a form on my website

Hi,

Like the title said some user have reported a 401 error while trying to accessing a form on our website. The problems seems to occur when the user has already filled the form and has a mkto cookie on his machine.

I was able to recreate the problem on my machine and was able to fix it by clearing my cookies but I cannot ask my customer to do that.

I ask our dev team to look into it and they came back blaming Marketo for the error.

Here's the link to the form:
https://www.exfo.com/en/resources/library-registration-form/?re=%2fumbraco%2fsurface%2ffile%2fdownload%2f%3fni%3d20623%2…

What can cause this and what can be done to fix that?

Thanks!

Jean-Fred