I'll answer my own question. Maybe it will help someone else. Unit can operate in 2 modes. MSC or auto detect. If you go into Settings/USB, you'll see these 2 choices. If the unit is in MSC mode, you cannot delete some MP3 files (in the Media folder). Make sure you are in Auto Detect. Thank you Sansa technical sup.
I originally loaded MP3 files onto the unit by copying and pasteing files in windows explore. I think I copied them to the media folder. Subsequently I copied addional files using Music Match. I was able to delete those files using Windows media player, but I cannot locate the original 1.4 GB of files I originally loaded. I do not see the Media folder in windows explore. The device properties shows 1.4 GB of memory used, but I cannot locate to delete. I am willing to reboot the unit to loose the files, but do not know how. There is nothing in the users manual regarding this, and SanDisk technical has been no help. Any ideas?

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