credit card number is invalid

From: carrie (
Date: 08/20/02

From: "carrie" <>
Date: Mon, 19 Aug 2002 17:53:20 -0700

Every time I order from it tells me my credit
card number is invalid, but I use the same credit card
number on other sites and don't get that message. If I
have my brother order and use the same credit card from
his computer to it goes through. I'm very
confused. Anyone know what to do/