I have exactly the same problem, i have tried everything and still doesn't work in my DSi with v1.4.4U.
http://down4.nds9.cn/r4isdhc-sliver/NewR4isdhc-sliverEnglish2.02.rar
This is the lastest firmware for the R4i SDHC STL Lite and my DSi still doesn't recognize the card.
:(