Someone commented this morning that they were having trouble with Paypal today - might be worth dropping them an email. I'm waiting for a buyer to pay, perhaps they are having trouble too.
My PayPal account takes money direct from the PayPal balance first if I ask it to, but you ought to have the option of using an alternative card if you've already registered it with them first.
Suggest you contact the seller and tell them PayPal is playing up, then they won't think that you are being slow in paying, I know I would appreciate it if it was me waiting for payment.