You must have statically configured ethernet interface to setup dhcp server.
Reconfigure ethernet interfaces...

 
General settings
 
  Enable DHCP server
 
Interface:
Starting IP address:
Ending IP address:
Address expiration time:
 
Information provided for clients
 
DNS server:
Search domain:
Default gateway:
 
   
Static addresses

  IP address MAC address Computer name



New static address:

IP address:
MAC address:
Computer name:
 
 
Current dynamically allocated addresses

  Computer name MAC address IP address Expiration time