1. On the affected Mac open System Preferences->Network pane's Advanced button. In the Advanced drop-down click on the button for 'Renew DHCP Lease'.
2.
Reset Your PRAM to see if it helps.
3. Go back into System Preferences->Network pane and at the top of the pane use the 'Location' drop-down bar to make a new custom name Location name. After making the custom named location don't forget to 'Apply' button to save everything. Don't worry because any custom named Location will work just like Automatic.
See if any of these steps help.