backup share point with backup.exec 12.5

Hello,
I have a agent  for share point and I want to backup a share point server, but i have a few quastions, please.

in a job selection on the backup.exec, i go to microsoft share point server farm and klick on add server farm.

I try to write my share point server name or the ip address and get this error: "non of the web servers for the specified server farm could be accessed".

what should i do to add my share point servers to a backup job?

my share point servers are in DMZ and there a rule in my firewall to confirm the connection.

thanks,
tali