Thanks for the advice.  I think I found out what the problem was.  Although I had my desktop PC set up correctly, my laptop (which I used to keyword everything during my recent trip) was not.  I wondered about how to fix this for a while.  Whilst the correct IPTC/XMP information was appearing in PM there was nothing in NX2.  Eventually, I discovered that if I selected all the files and did an "Apply Stationary Pad" using my correctly set up PC , all the keywords etc were now in a form that NX2 could read.  
I've now set up the laptop correctly so hopefully I'm sorted now.  
Thanks for your help.