If DHCP on your SBS fails to start due to:
Event ID : 20036 Source : DHCP Server Description: The DHCP Server is shutting down because another DHCP Server with IP Address <IP Address> is active on the network.it is due to having another DHCP server on your network.
SBS automatically installs and configures DHCP. You can not have any other DHCP server on your SBS network.
Multiple DHCP servers are only allowed with the full retail version of Windows NT Server and/or Backoffice Server.