Snapshot backup failed

Hi,

I am getting EC 156 while taking backup of Windows server.

Master Server Version = HP-UX (7.5.0.6)

media Server Version = HP-UX (7.5.0.4)

Client Server version= WINDOWS 2008 (7.5.0.4)

(156) snapshot error encountered

Let me know if any other information is required.

Can you tell me what needs to be done in this case.

Thanks in Advance