okay guys, listen up. I, from hereon forth, will speak in simple terms which may not be factually correct, but serve as a better way of understanding said information.
Before the 1.4 update, every flashcard could have any random icon it wanted to have. The Acekard had an acekard logo, the SC had a supercard logo, the R4 had an r4 logo etc.
After the 1.4 was rolled out, the NDSi started checking the logo information. If the logo didn't match up with a list of known games or was blacklisted the card was not allowed to initalize and boot up the firmware. This essentially disabled every flashcard out there.
There can be no firmware update for this, since the cart doesn't even boot the firmware in the first place. The cart gets inserted, the NDS sees that it is a non legit retail cartridge, and disables it.
Now the clever people that made the flashcards came up with a solution. They took the icon from a legit game, and released a software that would flash the cartridge itself, not the firmware. For that flash to be executed, you load a special application onto the memory card, and insert the card into a NDS that is able to run it (1.3 DS lite). Then the software changes the acekard logo to a legit game icon. Now the NDS will think that this is a legit game, and allows the cartridge to initialize, and thus booting the firmware.
If your card shows up as a legit retail cart (ALEX RYDER, FISH TYCOON) then everything is okay. If your cart doesn't start after being selected, you have other issues, like uncompatible firmware, need to format the SD corectly, wrong filesystem etc.
In case of doubt, do a full format with the Panasonic SD Formater, and do a full erease with size adjustment on, and then load a clean copy of your firmware only onto your cart. Also make sure the system files (the .nds) have the filename that your flashcart will be looking for upon intialization. If your card is looking for _SYSTEM_.nds and your file is named akmenu.nds then it's not going to start up.
Also you cannot change the icon. No you can not change it. The icon can not be changed. It is not possible to change the icon. The icon may not be changed.
There. Hope i made that clear.