1.40 NXS2 big bug

Have you tried to repeat it after a hard reset?  Also does it happen when the SP1 is not connected?

@Paola > There was never any guarantee made of compatibility between the CDJ-2000NXS2 and Traktor. It is up to Native Instruments to implement HID support for the player, not Pioneer DJ. Our product sends MIDI signal, which can be used with Traktor, or you could use the player with timecode to manipulate software playback.

If you are having technical problems with your player, we recommend contacting Pioneer DJ technical support in your region to have the unit inspected and/or serviced.

@Christian > Have you been able to reproduce this error?

Also, a tip for future - when a USB drive is connected, before powering down and potentially corrupting the data on the drive, try pressing and holding the "STOP" button for the drive. If that works, great, if not, then fall back to the worst-case-scenario of a hard power-off.