Unable to backup to SmartDisk with stage and store located on UNC attached storage (4032555)

Cannot backup to SmartDisk with storage pools hosted on ExaGrid NAS.

SmartDisk superserver trace shows there are problems modifying directories, deleting files and accessing meta data.

Reinstalling SmartDisk shows not all files are removed from stage and store locations.

Truing to delete the files manually fails.

Checking SmartDisk user access to the configured UNC paths on the Exagrid  NAS storage appears correct.

From binary log:

Job Message      2019/02/13 14:40:41       68             Media   SRVDPS465       Job has been assigned device 'SmartDisk - srvdps465'

Information        2019/02/13 14:40:41       68             Data Plugin        SRVDPS465             Connected to DAV server 'SRVDPS465' at address '172.21.129.7', port '37453'

Error     2019/02/13 14:40:41       68         Data Plugin   SRVDPS465       DAV server returned error: 'HTTP/1.1 404 Not Found'

Error     2019/02/13 14:40:41       68         Data Plugin   SRVDPS465       Error while closing the backup stream

From superserver trace file:  

0             FILEMANP           ???         87               155142634422  Failed to change mode of directory '\\?\UNC\172.21.129.5\NetvaultShare\Stage\diskmanager' to 504

0             DSTORAGE         ???         2               155142634422  Failed to created directory '\\?\UNC\172.21.129.5\NetvaultShare\Stage\diskmanager'

0             DSTORAGE         ???         7               155142634422  Failed to create Storage Volume root directory '\\?\UNC\172.21.129.5\NetvaultShare\Stage\diskmanager'

0             FILEMANP           ???         73               155142634422  Failed to delete file '\\?\UNC\172.21.129.5\NetvaultShare\Stage\diskmanager\volume.meta.__stnzwrt' : 5:Access is denied.

0             STNZFILE             ???         103               155142634422  Failed to delete '\\?\UNC\172.21.129.5\NetvaultShare\Stage\diskmanager\volume.meta.__stnzwrt'