From what you say, it would seem that you just transferred the file from your PC to the SD card, using either the 'Drag/Drop' or 'Copy/Paste' facility within Windows. It is not possible to transfer files using this type of procedure. The correct file transfer process creates additional 'control' files which the keyboard needs, in order to read the 'Song' files.
You must use either the 'Song Manager' program, supplied with your keyboard or the recently released 'SD Explorer' program.

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Willum
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Willum

After silence, that which comes nearest to expressing the inexpressible is Music.
Aldous Huxley
( especially when the music is played on a KN7000....)