First you should know the r4 sdhc card is made by r4i-sdhc, then visit the official website to download the latest kernel, and unzip it to your desktop, then copy all unzipped files to the root directory of SD card. If it still can't working, just wipe the metal trip with clean and dry cloth, and then try again. It should be work now.
Owner of an r4i-sdhc 3ds rts flashcard here. I bought my R4 3DS RTS card from http://www.r4flashcart.com/9-r4i-sdhc-3ds-rts-flashcart-for-3ds-xl-3ds-dsi-and-ds-lite.html have yet to have a problem with it, so I would recommend this card to anyone and everyone that's looking for a good 3ds card.
