Tracks not loading

Hi

I have a XDJ RX version 1 and I am now finding that tracks are not loading from the USB. I get a loading message but then nothing happens.

I have found that by toggling the digital/phono switch this usually causes the track to load eventually. It is all pretty random as has happened with different USB's and the tracks involved sometimes load o.k so it doesn't seem to relate to the file. I have the correct firmware that dealt with an issue described as this on the machine already.

Any suggestions on what could be causing this?

Thanks