Thanks for the reply.
Nothing has changed as far as I am aware, I was ripping the 3rd CD, please be aware that the HDD and the CD reader are both USB3 devices, if this makes any difference, As I was ripping the last CD, I noticed that the HDD files all had a RED X next to them.
The PC has 2 x USB3 ports, the HDD was plugged into one port and the CD Drive into the other.
The HDD port/cable is never disconnected, I can access the files on the drive as normal.
I have imported another album from the same HDD after ripping the CDs, this album plays fine. So I can play the 3 x CD and 1 x HDD album, all the initial HDD files still have a RED X next to each track
So even more confused now.
Any help appreciated