sd(not the sdhc for r4/acecard.) card cannot be use - nintendo dsi

pls help me that when i insert the sd card in the slot, it says it recognizes the card and after that it also says that the sd card cannot be use.? what is this.. pls help me..
Post Merge: [time]1300872100[/time]
pls help me guyz.. i just want to use it.. T_T