Again, thanks everyone for your help and advice.
I uninstalled the old version of ViewNX2 and installed the version of NX that came with the camera (although I don't understand why this should be different from the existing version for which I had executed all the updates) and yes, LR can now read the RAW files.
I also tried converting the files originally imported in NX using the old version, but no luck - they are in an unsupported format for the DNG program. I guess I'll have to try and fix the corruption using the above link. Luckily they were not that important.
