Backup Error failed through VCenter but success through ESXi

Hi all,

Backup Exec 2010 R3 SP4  is installed on Windows 2008 R2.

There are totally 4 nodes of ESXi, namely E1, E2, E3 and E4

E1 / E2 - ESXi 4.1 u2

E3 / E4 - ESXi 4.1 u3

vCenter - version 4.1 @ WinXP

Problem encountered:

- we cannot backup VM @ E3 / E4 while we can backup VM @ E1 / E2 through VC

Error Messages:

V-79-57344-38277 - Unable to open a disk of the virtual machine.

VixDiskLib_Open() reported the error: You do not have access rights to this file

- for additional information we can backup VM @ E3 / E4 via ESXi

Can anyone suggest what action we should take to solve the problem we cannot backup VM@ E3 / E4 through VC ?

Regards,

Thomas