Hi
Actually, the payment is handled by Paypal, so It is something with the paypal account whicn receive payment. To solve this issue, there are some ways :
1. Please try to use a different paypal account in Payment Form to receive payment. If the payment works well with the new paypal account, then It must be something with the settings of the current Paypal account . Maybe you can contact Paypal for support .
2. If the currency which users use to pay is different from the currency of the paypal account receiving payment, Paypal will mark the payment as Unclaimed. In this case, you can accept or deny the payment .
Please do some checks and give me some more clues. I am available for checking it with you via Skype, YM, MSN or Gtalk .
Thanks,
Tuan