Write to Data domain Cifs share but "Disk volume is down(2074)"

1) [root@blxecnbumast ~]# bpstulist -label ashrmmnt01_exch01_dd860_mtree -L

Label:                ashrmmnt01_exch01_dd860_mtree
Storage Unit Type:    Disk
Media Subtype:        Basic (1)
Host Connection:      ashrmmnt01.active.local
Concurrent Jobs:      1
On Demand Only:       yes
Path:                 "\\10.76.12.122\mtree_blxecnbumast_exch01"
Robot Type:           (not robotic)
Max Fragment Size:    10240
Max MPX:              1
Stage data:           no
Block Sharing:        no
File System Export:   no
High Water Mark:      98
Low Water Mark:       80
Ok On Root:           no

2) all the NBU services are running with domain account svc.exchangerepmgr instead of local system

3) I log in media server via domain account svc.exchangerepmgr and I can write to the Data domain cifs share......but it prompt for username/password at the first time

4)both the "nbemmcmd -listhosts -verbose " and  "nbemmcmd -getemmserver" completes successfully

[root@blxecnbumast ~]# nbemmcmd -getemmserver
NBEMMCMD, Version: 7.5.0.3
These hosts were found in this domain: ashrmmnt01.active.local, lxecnbumast.active.tan

Checking with the host "ashrmmnt01.active.local"...
Checking with the host "lxecnbumast.active.tan"...

Server Type    Host Version        Host Name                     EMM Server         
MEDIA          7.5                 ashrmmnt01.active.local       blxecnbumast.active.tan
MASTER         7.5                 lxecnbumast.active.tan        lxecnbumast.active.tan

Command completed successfully.