Difficult to say if you have already tried all of the suggested troubleshooting.
Did you install yesterday’s update to Lr Classic v7.2? If not, launch Creative Cloud and go to the Apps tab to check for the update. If no update is showing launch Lightroom and try from the menu:
Help >> Updates
Are you sure the version of OS X on your Mac hasn't been updated without you knowing about it?
Can you open LR at all?
The update released yesterday for LR might of reset the GPU to ON, Checked. If you can't start LR to check that then you will need to make the change by editing a text file.
See solution 2 on this webpage.
Thank you for the suggestion, I just checked 99jon and all is up to date, so very odd. Only update I have available is Lightroom CC, which I am not using.
If the CC DTA is showing an Update for LR CC that means you do have it installed. I suggest you uninstall that if you have no plans on using it. You can do that from the CC DTA.
Hi, yes 100% not done without me knowing. I can open Lightroom and it all seems to work fine, just comes up with the error each time I open it up. I looked in the preferences and the GPU box is unchecked (which I presume is correct?).
Oops, meant to say it states "Install" on Lightroom CC, not update, sorry for the confusion