Error 10525

i get this error trying checkout with paypal.

There was a problem connecting to PayPal to setup your purchase. Please try again.

* 10525 - Invalid Data - This transaction cannot be processed. The amount to be charged is zero.

according to the paypal api reference it means.

10525 Invalid Data This transaction cannot be
processed. The amount to be
charged is zero.
The merchant entered a amount of zero

I'm running latest versions of marketpress, framemarket

http://www.ybrmarket.com.au/