I had this same issue the last time I ordered something.
I have 26 items in my shopping cart - a mix of .pdfs and physical products.
When I click "Proceed to Checkout", I am sent to a page to re-enter my password. When I re-enter my password, I am kicked back to the main Paizo page. So I go back to my cart and the whole process repeats itself.
I have attempted to checkout numerous times and the same thing happens every time.
I have attempted the purchase from three different computers (PC and MAC) with the same results.
I have logged out and logged back in. Still no joy.
The last time this happened, I sent an email to customer service. I never got a reply. A few days later the items (they were all .pdfs) just appeared in my downloads page without an explanation.
I sent another email to customer service today.
I figured I would post here as well.
What's going on? Am I going to have to go through this every time I try to purchase something?