I tried the 4.2.19-T4 together with OSX 10.6.8 (Snow Leopard) and using AFP.
From time to time I received the Message "Something wrong with the volume's CNID DB" from the Frontview Web-Application. When I received this popup, I typically made some very intensive data-transfer (the initial fill of the NAS).
In Addition to the Popup Message the transfers are aborted.
--> Copying 200GB Data with > 100K Files was not possibe, the transfer aborted. Also a second try failed.
--> Backup to an attached USD-Drive (EXT3) also failed with unspecific error messages.
After that, I switched back to 4.2.17 and all File-Transfer and also to Backup worked as a charme. And I never got this Popup again.