Problems making conference payment online

I'm having trouble making my payment online with a credit card. I have logged into my account and selected the 'make payment' option. It displays my invoice details correctly, but when i click on the 'make payment' button it comes with an error message every time. Is anyone else having this problem? Is there another way of paying online? (i'm reluctant to do a direct bank transfer because i will incur additional bank fees for the international transfer)