I've been making sales for a couple of months with no error messages and I hadn't changed anything. Sales had been going through today as well so I don't see what I could have done that is wrong.
I did try turning the pro billing off in the e-junkie panel after your message here but everything disappeared from the cart window on my web site and it just said checkout with no visible logo, so I clicked it back on. After that I took the dog for a walk and when I came back there had been 3 successful sales so this is a real mystery. I shall try contacting PayPal if I get anymore customers talking about error messages.