You are going to exit Thailand in Nan province at Huai Kon? As far as I know there is no Lao Visa on Arrivale available there. So unless you belong to the few nationalities that not need a visa for Laos you will have a problem entering Laos there.
Thanks for your reply. I used it before and now suddenly it works again. Probably a glitch in the system. Hopefully it will not return. For the rest the website works good (although a bit weird way of user-interface).
I did this a few times and returned within 30min. No problem. I once asked the Thai IO if I really had to waste money and time on going to Laos. Unfortunately I had to really cross the border into Laos.
Thai visa center - visa agent ...if you made so much bookings (and money) then you could offer the moderators of this forum an official job with work permit.