Given that DSi is in the error message, I can't see how you would be getting in on a DS Lite.
Yes, that's the error message you get when you attempt to use a non updated Acekard on a DSi which has Firmware 1.4.
It doesn't do anything when you press (B) because it needs to be performed on a DS Lite or DS PHat, as in the guide. The DSi won't allow you to swap carts, and it just sit there on the screen which asks you to press (B) after swapping carts.