Why does my 3DS claim I have no space on my 4GB SD card while it looks empty?

I have a 4GB SD card, but when I try to update a game on my 3DS it always says "You need x more open block(s) to download this.". When I look at my Data Management, the software, extra data and DLC on the card are all displayed as empty. Why does my 3DS claim that I have no space on my SD card?

Photos of the screen of my 3DS


Solution 1:

SD cards can contain data other than 3DS-specific files. Free up some space in your SD card by using any file explorer, such as connecting it to a computer.