PayPal has posted notice of a major disruption to their service currently making checkouts unavailable for PayPal Website Payments Standard and Pro:

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https://www.x.com/community/ppx/systemstatus/mts_updates/blog/2011/02/18/notification-major-impact-to-apis-and-wwwpaypalcom--feb-18



Notification: Major impact to APIs and www.paypal.com - Feb 18



Posted by PayPal_Updates on Feb 18, 2011 12:32:48 AM

NOTIFICATION: Payments via API and www.paypal.com are unavailable for most customers.

Sent Feb 18, 12:29 AM PST by VB



Start time: Feb 18, 12:11 AM PST (Feb 18, 8:11 AM GMT)

Estimated time for resolution: TBD



At this time, there is no alternative work-around.