I have checked the credit card log and can see that no authorisation refusals have occurred since 7th February. I've also just done a test purchase (using a mastercard) and everything worked perfectly for me.
This leads me to believe that you card failed pre-authorisation checks. These checks are for things such as an incorrectly entered card number or an invalid card type and are done before a request is made to the card issuer for authorisation.
If you can give me more details of the card type used and the actual error message received, I can give you more information about precisely why your card was refused. Use the contact form at: http://excelcentral..../contactus.aspx for more privacy and security.