I have it too.
ISSUE: new mp3 files copied from PC to Sandisk player (Clip Sport Plus)/Music folder not recognized as songs. When located in folder and clicked Play > message ‘File format not supported’ displayed.
Root cause: Windows OS applies encryption to any new folder/files by default. Encrypted files (mp3, wma) not recognized as playable when moved to Sandisk player.
SOLUTION: > Right click a song file (mp3 or wma) on PC
Select Properties
Click ‘Advanced’ button for Attributes
Uncheck ‘Encrypt contents to secure data’ checkbox
Click OK
Click Apply
Click OK to close Property popup
Copy file to Sandisk/Music folder
Check if it still has ‘Encryption’ property unchecked
Allow Sandisk player to refresh media
Result: new song should appear and play
NOTE: Same fix can be applied on a folder level containing multiple media files then the whole folder can be moved to /Music location
