While the Archive bit backup type is the preferred type for Windows backups, the need to modify the archive bit on the source leads to three requirements. If they cannot be met, the Timestamp method should be used instead.
That ReadyNAS has both read and write capability for the source location. For example, this excludes all NTFS volumes connected via USB (NTFS on USB is supported only in read-only mode), but not FAT32 volumes connected via USB.
That ReadyNAS has write access for the source location, specifically the type that allows it to modify the Archive bit.
That ReadyNAS is the sole backup solution using the Archive bit method for the source location. Failure to meet this requirement will lead to incomplete backups for one or both backup systems.