WooCommerce issue, "sorry your session has expired. return to homepage"

i am having this session issue, i am using 2 plugins.

Single Page Checkout & WooCommerce.

I made the frontpage a single page checkout page, and i modified the plugin bit for my needs, anyway, it all works fine when i am logged in.

But when i am not logged in, i receive this msg: "Sorry your session has expired. return to homepage".

This appears 1 sec after the checkout elements are loaded, it seems to be javascript that prompts the msg.

As i see it i have 2 options.

1) Find the issue, which is turning out to be quite hard. 2) Create an account that i auto login every single user to. Since the error does not appear when the user is logged in, i would have to block the admin pages for the user too, but this seems like a major security risk.

Does anyone know what controls WooCommerce sessions? And why this error occurs?