Seems like the catalog got corrupted.
Launch Lightroom with the control/command key pressed and choose to create a new catalog.
Then, go to File> Import from another catalog and choose the main catalog to be imported from.
If this does not work, then you might have to look for the last backed up catalog.
Thank you for your suggestion but this doesn't seem to have worked. I can no longer get creative cloud to open and when I use the lightroom short cut the same error occurs. The programme was working fine until the last update. if you have any other suggestions I would be grateful.
Would suggest you to launch with the Alt/option key pressed.
Do you have a catalog backup which was backed up recently?
Try launching that backup catalog by manually browsing to the location of that backup.