The R4i Red card might be a fake (the genuine one shows r4i-sdhc.com on the box, note the hyphen!), and if you've updated your console to the
latest 1.4.2 or 1.4.3 firmwares it's unlikely to work. Check out R4 DS Revolution Cards
at www.r4dsrevolutioncards.com (info site) to differentiate between different versions of R4i cards
and make sure you buy a genuine one!
A lot of the fakes will indeed work when you buy them but as soon as you update your console they'll stop working.