Same here. Started with NV+ and RAIDiator 4.1.6.
Had a disk fail, replaced it with the WD20EARX, and all I got were a bunch of these two errors:
The disk attached to channel 4 could not be used. The most common reasons are RAID resync in progress, faulty drives, and disks that are too small to be added to the array.
A SATA reset has been performed on one or more of your disks that may have affected the RAID parity integrity. It is recommended that you perform a RAID volume resync from the RAID Settings tab ( accessible in the Volumes page => Volume tab in FrontView ). The resync process will run in the background, and you can continue to use the ReadyNAS in the meantime.
Restarting would not help, doing a hot-swap would not help. The unit kept reporting the drive as DEAD (and unusable).
In an effort to reproduce stodge's success I left the new drive in the bay, updated to RAIDiator 4.1.9, rebooted, and it immediately started initializing the new disk.
Disk initialization started. The estimated time of completion is 17 hour(s) and 39 minute(s), at which time you will be notified via email. You can also check the progress in Frontview in the Volumes -> RAID Settings tab. Please do not shutdown the system while the initialization is in progress.
Very happy to have found this entry. Hope this helps someone else too.