So I'm copying files onto an SD card to go into a digital photo frame and suddenly get this message:
Odd. I check whether there's space on the card. Loads. I check that the file names aren't too long somehow. Nope.
Turns out that the SD card is formatted as "FAT" -- the old, very basic DOS file system -- and there's a limit to the number of files you can place in the root directory. Moving the new files to a new subdirectory solved the problem. Great.
Now try explaining that to my Mum. Particularly when she's received that wonderfully useful error message!