When I click on your link, I don't see any error. It is (probably) because you are trying to you "use" your own referral code, which does not make sense. Other users will not see such error.
When I try to use my own, I see the error too. You can re-check with mine: http://project-gc.com/r/f2487a39
It should work the same way for other users with your code.