SD Card incompatible: Could I be doing something wrong?

I have a Kingston SDHC Class 6 4GB card. It is listed as compatible on the Wiki, but does not work when I try to load BootMii using it. The drive flashes and boots to the system menu as though no card were in there. Could reformatting possibly help? Or is the Wiki wrong here?

Check the SD card for a bootmii folder, and in that "ppcboot.elf", "armboot.bin" and "bootmii.ini

Are you sure your card is genuine? Where did you buy it?

Are you sure you have all the correct files on your SD card?
Also, are you sure you even installed bootmii as boot2?

Try reformatting with different cluster sizes, file systems and stuff until it works.