network read failed (42)

hi
i am facing some problem in veritas netbackup 6.5.2
i have 3 servers which are configured as media server.
now one server with windows platform is not getting backed up from past 2 days
and giving error code 42 network read failed

i checked network settings and host files
ping test from host to server and vice versa.

and i checked some log and in bpdbm log file i found msg that is
db_valid_master_server: tcsc-ads.tcsckandla.com is not a valid server

plase provide help with this issue
i am new to veritas netbackup.


Thanx