Is it possible that my firewall or proxy server is interfering with communication to Acromag's Ethernet I/O Modules?
Yes. Many industrial networks use a Proxy Server to create a firewall. With this configuration, the Proxy Server prevents the computer from communicating with the module. If using the Internet Explorer browser, go to the top tool bar and click: Tools / Options / Connections / LAN Settings. Then Uncheck the Proxy Server.