Logging on

When am at the login screen with fields,Username,Password and Domain. With have a DHCP environment back here. The errors are as follows:
1.System has detected a conflict IP address xx.xx.xx.xx with system hardware address 00:00:39:x.x.
2.You are not authorised to log on from this terminal.
What is happening?Settings in the user domains are all fine.
Thank you in advance.