This is an old thread but thought id add my findings as it may help some people.
As we know most if not all R4 cards these days are clones however I have ordered many cards at some really good prices for instance $7 for card and 2gb memory delivered and never had a broken one.
Ok might have taken me a bit longer to get the card working as there are so many kernels out there but you will get there in the end.
Particularly for Barbie's problem i had same issue. The card is probably not broken.
Simply reformat the card fat32 file system apply the kernel again (R4i English v2.10T06 ------?2010-06-24?) and try again, will find that it loads ok.
You know when a card is duff or incompatible when you insert card into DS and console does not recognise it. If it starts to load and you get errors or black screen/white its nearly always a kernel problem. I now by a rule of thumb also reformat card before trying a new kernel.
No doubt people will flame me, saying its rubbish and not to use clone cards blah blah blah..... however maybe if Barbie had tried this first could have saved a few coins before buying another card. Nothing to loose by trying.....
Cheers
Scar1