Did you recently sit down at your Windows workstation to find that you could no longer access a mapped drive?  Did you disconnect the drive and reboot, thinking you would just remap it, only to find that the drive letter is now in use by a "Removable Disk (G:)" or other designation?

This is precisely why I start my mapped drive letters at M and above!

But, if you didn't do that, and you can't change your drive letter for some reason (maybe you have some network application that won't let you change the drive designation?), you're going to have to change the drive letter used by the SD card reader.

It sounds harder than it is. 

Run regedit and find the following key.

    HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices
    Right-click "\DosDevices\G:" and then click Rename.
    Rename it to "\DosDevices\M:" or your preferred letter.
    Restart your computer and remap your drive.