Please turn off the Graphics Processor from the Lightroom preferences.
Go to Lightroom Preferences from the Edit menu
Click on Performance tab
Uncheck the Graphics Processor
Let us know if that helps.
Yes, unchecking the Graphics processor seems to have worked - initially
the check box was greyed out but when I opened a new catalogue and tried
again the problem seems to have gone away. I tried to reply via your
link but there was no correct to click.
Thanks for your help,