The update cannot be installed because some files could not be copied. This is usually due to inconsistent file permissions.

WordPress core updates first copy the new files into place. When some existing files cannot be overwritten, WordPress stops and shows this message, which names inconsistent file permissions as the usual cause. The files that failed are listed after the message.

Common causes

References

1. Changing File Permissions (Advanced Administration Handbook)
2. Upgrading WordPress (Advanced Administration Handbook)

Rather not fix it yourself? Let WP119 handle it automatically.

Wrong file permissions are handled automatically: the system resets them to safe, working values. Fixes are made on a copy of your site in the recovery station and written back only after re-verification passes. In your site’s database, the protected tables (members, comments, orders and form submissions) are copied as structure only. In SSH and FTP mode, the system creates a pre-recovery backup on your host before writing back and restores from it if verification after write-back fails. If the recovery cannot be completed, the recovery fee is refunded in full.

1. Initial assessment: Site URL entry
2. Copy to the recovery station: Work on a copy
3. Diagnosis: Item-by-item checks
4. Recovery and verification: Home and inner pages
5. Write-back or delivery: Only after verification passes