I believe you can scan using network and twain setup.
To make sure firewall is the one causing the problem, please disable the firewall and attempt scanning so see if it works. If it does than we know is a firewall config issue.
If you installed any scanning application, please make sure that you add the application you installed to the firewall exceptions.
If you are using network scanning, you will need to identify the protocol FTP (21 or 22) or SMB (137 or 139) and allow the ports.
You also can get more detailed info on the Administrator Guide: Page 65 and 75.
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