The IP address that the _Symantec_netBoot_Interface Service is attempting to create a socket connection on is not the correct IP address for the server on which it's attempting to run.
This is most common when the Server's IP address was changed for some reason.
In the SBS directory (default "C:\Program Files\Altiris\Altiris Agent\Agents\Deployment\Task Handler\SBS") find the file "initialPXEConfigPath.txt".
In this file locate the following lines:
Change the IP address values to the correct IP address of that server.
If the lines are not in existence, add them to the file. The resulting file should have the following entries (with the approriate IP addresses for your systems). If 'Server_Ukn_Enabled = True', two additional lines will be added to the end of the file.
Mtftp_Root_Folder=C:\Program Files\Altiris\Altiris Agent\Agents\Deployment\Task Handler\SBS\Images
Server with net boot (PXE) services installed