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@Adrian > As @Spark972 says, if the drive was a rekordbox export device, there would be no analysis required on your computer unless your friend was trying to import the songs from the USB drive directly into your collection.
As I say with many things in life, it it only happens the one time, it could just be a fluke - but if you are able to repeat the process and know what you did was the correct method of operation, and it fails again, then it's likely a problem, and you should let us know.