Can’t purchase articles in the marketplace

I'm trying to make a purchase in the marketplace for some articles. Each one I've tried I click on the buy button which takes several seconds to finally load a pop-up window asking for my user/pass to paypal.
No matter how many times I try to login it will not allow me to login. I open a new tab and go directly to paypal.com use the same user/pass and I can log in just fine. So I know the login is correct. I'm only having Paypal issues on DP.
Any suggestions?

See original post by WoodiE55