PayPal experienced some issues yesterday, leading to PayPal payments on the Marketplaces being declined between 17:00 and 19:00 AEDT, 28/01/13. You can read more about this issue here.
We are happy to report that PayPal transactions are now working, and payments are being processed normally. We are currently working to identify all users that were affected by this issue and then plan to complete the transactions i.e. process the payments and deliver the items. We do not have a timeframe for this fix yet. We will advise once we know, via this forum post.