Had to do a factory reset on PC due to other problems.
Reloaded LR 6 ex disc. LR seemed to pick up the existing catalogue automatically with no problem. Older photos seem to be OK (Nikon D5000) but photos taken on Nikon D7500 now give error message "file format not supported", when loaded into Develop module. They can be viewed in Library mode These were previously edited in LR with no problem.
Any suggestions on how to resolve this problem. These are NEF files
If you used the disk, the installation will be for Lr 6.0 whereas the final release was Lr 6.14 so you need to update the software.
This is a user to user community. For some issues it will be necessary to contact Adobe directly. Click the following link and scroll down the page to Individual. Then click “Sign in to contact us” It should be possible to start an on-line chat with Adobe Support. Have your serial number to hand. Make clear that you are not looking for support for an older product but need a download link for the final version of Lr 6.