The first thing to try with any PayPal error is to clear your browser's cache, cookies, and history. You'll need to refer to your browser's documentation if you don't know how to do this.
One possible reason for an error is that PayPal is unable to communicate with your bank. There are other reasons that we are not familiar with. If you are still getting the error, you will need to contact PayPal's customer service to find out the reason for the error. Alternatively, if you have another method of payment available to you, you might use that instead.