The File Allocation Table (FAT), which tracks what files are where on the disk, how much space they take up, etc is corrupt.
Fortunately, there is a backup copy of the FAT on the disk, which Norton is offering to restore as the main FAT. Let it.
OnePlus 5 review
Alice Saey's mesmerising animation for Dutch singer Mark Lotterman
iPad Pro 10.5in (2017) review
Comment booster votre iPhone ?