"There is an IP Address Conflict with another System on the Network"

Is there wireless on your network?

I've had this before. There are probably two computers on the network that have the same name, so it's confusing the server. This happens even if one of the machines is turned off. Delete both machines from the network, reboot them, and rejoin them to the network with unique names, and you'll be fine.

I think a bit more information is needed.

What kind of router you are using?

It is possible that you can have reserved ip addresses or mac addresses on the router itself.

Is this on a wireless or wired network?

If you have the capability of both, then make sure the two interfaces are not taking up the same ip address.

You must be assigning the ip statically, or else if using a DHCP server, open up command prompt and type:
ipconfig /release
ipconfig /flushdns
ipconfig /renew
ipconfig /registerdns

If it is a wireless network make sure it is secured and people nearby are not utilizing your network.

Sorry for the brief response earlier, I knew I'd saved information on the fix somewhere.

Once a machine is on the network, its name is taken. Another computer cannot have the same name without causing problems with the domain controller. However, this problem may or may not occur immediately  it could take several days to appear. Here is where this came into play:

When Sales01 was retired and replaced with a new laptop, the new laptop became the new Sales01. The original Sales01 was shelved. Later, it was upgraded and redeployed as a new machine, FrontDesk01. Although the workstation was renamed, the network still recognized it as Sales01. As there was already a Sales01, access was refused. IT recognized it as an issue and flagged it as a low-priority issue to resolve, since no one was would be using FrontDesk01 until someone was hired. The issue propagated to Sales01, when the domain controller also started refusing to allow it access. This became a high-priority issue immediately.

If this issue arises again (a possibility given the departmental naming scheme), here is the way it is resolved:
1. Log into the server and delete the computer (not the user) account. This removes that name from the network.

2. Log out from the server.

3. Go to each affected workstation and log in as a Local Administrator (rather than Network Administrator).

4. Open the Control Panel and double-click the System icon. You may have to switch to Windows Classic view to see it. Go to the Computer Name tab.

5. Remove the computer from the domain by clicking the change button. There are 2 radio buttons, one for domain and one for workgroup. Select the workgroup button. Name the workgroup anything and click OK. This creates a bogus workgroup, and joins the computer to it  thereby removing the last trace of its connection to the network.

6. You may want to restart the computer, but its not always necessary.

7. Return to the Control Panel, System screen, Computer Name tab. Change the radio button back to domain and enter your domain name. Click OK.

This procedure removes the computer completely from the network, then rejoins it.