I reloaded the Mp3 files that didn't work and I can listen to them now. May be the files were corrupted when I copied them the first time.
Problem solved now
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Victor

Korg Pa3x 61 - Mediastation X76 - Yamaha Psr s900 - Korg Tr61 - Roland PK5A - NanoKontrol - Ensoniq SQ1 - Yamaha D85 organ