PayPal requires that Cookies be enabled in order to complete a credit card transaction.
If you get the "payment session has expired" message below, this is probably your problem.

  If you are using Intenet Explorer, you can allow Cookies by going to Internet Options under "Tools"

When you get the Options screen, go to the "Privacy" tab.

You must select "Low" or "Accept All Cookies", the next one down.  After completing your PayPal transactions, you can return your Privacy setting to where it was before.  I have tried the settings above this and would get the message shown at the top of this page.

Hope this helps,

Bob McCormack
BrownBag Data