This error is still an active issue. I've tried to checkout from multiple OS's, browsers, locations, systems, payment methods, and combinations of them all. My last several attempts were on Windows 7 using IE9, Chrome, and FF to no avail.
Regardless of configuration or payment type I receive the following error:
An Error Has Occurred
Either your session has timed out or an error has occurred.
If you were in the process of purchasing a new premium membership, a basic membership has probably already been created for you. Please log in using the username and password you supplied for your account. Once you have logged in, you may upgrade your account.
Otherwise, please click here to start the checkout process again.
Is there another place where this should be submitted to review the issue?