The message is “The network name cannot be found”
The most common reason is that CasaTunes is not set up to use iTunes Plus music. Open Casatunes Setup on the CasaTunes server PC (can usually be found on the desktop) and click on the iTunes Plus tab. Check the “Enable CasaTunesSync for iTunes” checkbox.

The message is “Logon failure: unknown user name or bad password.”
On the CasaTunes Server PC go to the Control Panel, pick Network and Sharing and turn off “Password Protected Sharing”

The message is “....access is denied…”.
Make sure all the computers on the Local Area Network are assigned to the same “workgroup” or domain. In Vista and Windows 7, you can check this by going to System in the Control Panel. In Windows XP, go to System in the Control Panel and select the “Computer Name” tab.