I've been storing some files on a MicroSD formatted to ext4 that I connect via USB. I tried to move a directory in it to an external hard drive, and I got
mv: error reading ‘/mnt/sd/Directory/xyz.mp3’: Input/output error. I tried to
chmod -R 777 the mount point of the sd (as root), and I got
chmod: changing permissions of ‘sd/Directory/xyz.mp3’: Read-only file system. I never did anything to make the filesystem read-only, and I've had no trouble with it before. The only thing that I can think of that's changed is the SD is usually
/dev/sdb1, and it was
/dev/sdc1 this time.
Running Arch Linux in Virtualbox on a Windows 7 host.