Sometimes when devices (pen drive) are added, the drive letter of other existing drives changes. Programs that reference the old drive letter will output an error message similar to the one you are seeing.
I overcome this by changing the drive letter of my DVD drives to "M" and "N", external storage HDD to "Z", and backup drive (external) to "S". Now when I insert a thumb drive (pen drive), it assumes the drive letter "D", "E", etc. and is consistent. Works for me.