ERROR: Sorry, we can’t complete your purchase at this time

[Monichiwa]

I would like to buy some stuff with the money I have in my paypal account, but everytime I try to log in this message appears:

Sorry, we can’t complete your purchase at this time

Please return to the merchant and choose another way to pay.

And it doesn't let me pay or do anything else. Why is this happening and how can I get rid of it?

Thanks in advance.