One of the reason for this could be that IPv6 is enabled on the remote machine.
To resolve the above error, disable the IPv6 as explained below.
On Linux/Suse:
Linux has Internet Protocol Version 6 (IPv6) enabled by default, almost all distributions enable it.
1. To disable it on Linux please open modprobe.conf file (Red Hat) and add following lines:
# vi /etc/modprobe.conf
alias net-pf-10 off
alias ipv6 off
2. Save the file.
3. Restart the RALUS process.
4. Try to select the Linux machine from Backup Exec.
In case if the Alias entry is not available
1. Open terminal and run the following commands
echo "alias net-pf-10 off" >> /etc/modprobe.conf
echo "alias ipv6 off" >> /etc/modprobe.conf
2. Restart the server
3. IPV6 should be disabled now.
On Mac:
1. Go to System preferences and select "Network"
2. Select "configure IPv6" and disable IPv6.
3. Restart the MAC Agent.
4. Try to select the MAC server from Backup Exec.