backup partially successul with WRN - can't open file: System State:\System Files\System Files (WIN32 -536805667: Unknown error)

i encounter an error while backuping several Windows 2008R2 clients with error message :

WRN - can't open file: System State:\System Files\System Files (WIN32 -536805667: Unknown error)

Master server is Netbackup 7.1 on linux

Clients netbackup version is 7.5

Clients OS version is Windows 2008 R2

backup object is ALL_LOCAL_DRIVES

anyone have an idea