If you turn on Windows Firewall and then select Allow this computer to use a network scanner in the Scanner and Camera window in Control Panel, you cannot use the Scanner and Camera Wizard to access a network scanner.
This problem occurs because Windows Firewall blocks TCP port 21. This port is required.
To work around this problem, you must create a Windows Firewall exception for TCP port 21. To do this, follow these steps:
Click Start, click Run, type firewall.cpl, and then click OK.
In the Windows Firewall dialog box, click the Exceptions tab, and then click Add Port.
In the Add a Port dialog box, type Scanner and Camera Wizard in the Name: text box.
In the Port number: text box, type 21.
Click TCP, and then click OK.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.