Because something obviously is. I have an r4i Gold. I was using a 2GB microSD card. Putting it the USB adapter and attempting to open it on a Windows 7 PC results in a) explorer eventually freezing and refusing to restart until the USB adapter is removed or b) it refusing to recognize the USB adapter at all. I can access it just fine on my Mac. However, if I copy files to the card and then delete them, it does not free up space on the card. That space is forever gone. At best, attempting to install firmware gets me an endless loading screen on my DSi. At worst, the DSi pretends there's nothing in the slot. I posted here before and was told my microSD card was bad. I bought a new 4GB card and am having the same problems. So either I have the worst luck with microSD cards, or that isn't the problem. I want to give up now, but I feel like I've spent too much time and money already...
I've had the same problem. I don't know exactly what caused it, but I solved it by buying a new adapter/card reader. -- Edit : I should add that my card runs perfectly fine. Besides being unable to connect to the computer through the adapter, there was actually nothing wrong when I ran it with my DS. That was why I concluded that it was the usb card reader's fault. My symptoms were (I tried it both on a vista laptop and an XP desky) that the 'removable harddisk' window will just freeze when I click on it. Otherwise, the card ran perfectly.
If this problem persists, try a new adapter for sure. There is probably something wrong with your current one. When my MicroSD card was truly corrupt, nothing could read it correctly, nor could anything format it.
