OK, here is where I am at:
On vers 11 - after creating a new share on the nas and pointing a new bu2d folder at it, the bu went fine.
On vers 9 - I had done something similiar on this one, actually just deleted the .bkf files in the backup share on that nas (different location/different nas) then retired the media that those files corresponded to. The backups went ok until last night. The bu's were set to start overwriting the files last night, so that I would have a 7 day rotation. BU Exec deleted all the data in the .bkf file, then errored out. I ended up with a .bkf file with 0 bits.
This will happen on the vers 11 NAS too in 6 days when the settings allow it to start overwriting the files.
Here is the message from last night, it is slightly different from the one I was getting:
Final error: 0x40 - The specified network name is no longer available.
In version 11 I was getting this error, same exact symptoms:
V-79-57344-34036 - An unknown error has occurred.