open file problem with vss

Windows Server 2008 R2 Standard SP1, NetBackup 7.5.0.5 (client and server)

i have two servers having the above installations. both servers have all default configurations for both Windows and NetBackup.

when doing backup, server1 backup (all local drives) goes fine. but for server2, i get open file errors from Windows files.

Symantec has investigated the issue and concluded:

1. observed VSS snapshot issue for “C: Drive”
2. same configuration with other client server backup are working fine

some errors are,

7/1/2013 12:20:21 PM - Warning bpbrm(pid=2619) from client server02: WRN - can't open file: C:\Windows\System32\config\DEFAULT.LOG1 (WIN32 32: The process cannot access the file because it is being used by another process. )
7/1/2013 12:20:21 PM - Warning bpbrm(pid=2619) from client server02: WRN - can't open file: C:\Windows\System32\config\DEFAULT.LOG2 (WIN32 32: The process cannot access the file because it is being used by another process. )

the investigation took almost a month. appreciate for any help on this.