We're sorry to hear about the trouble you see while importing the files in Lightroom.
Which version of Lightroom are you using? Where are the images located? Do you see this error message with any specific file format? Can you please check if your already imported photos have the same file name as the ones you are trying to import? Or if there are files in the trash that you deleted with a similar name? If there are deleted files, they'll remain locally until the originals you deleted from the cloud are permanently deleted. Initially, deleted files are moved to the unique "Deleted" album, and they stay there for up to 60 days (to give you time to reconsider and restore the files if needed), after which they are permanently deleted (and would thus be deleted from the local store). However, you can manually permanently delete the images from the Deleted album during those 60 days (open the Deleted album, select the photo (s) and click on the trash can icon).