I have tried to update my firmware by putting USB in MTC mode then moving the m300a1.bin into the Sansa Clip Icon but when I move the icon to the trash and unplug the clip it doesn’t upgrade. I currently have version 1.01.18A.
Try using the Sansa updater on another PC, if possible.
The m300a.bin file must be unzipped prior to installation: is it about 6MB? If so, it’s still compressed, and the Clip can’t use the file. Also, be sure to drop the file into the root directory, and not into any of the folders.