The red light flashing means that the device is in Safe Mode, which has just enough functionality to be able to update the firmware. Usually the box would only enter Safe Mode if it detected that the firmware was corrupt, but by holding the button down for a very long time you manually forced it into Safe Mode. This will not harm your box in any way, but it will restore the factory default settings.
When you generated settings2.png, did you type the index.esp at the end of the URL, or did you enter the IP address and the URL updated itself? If the URL updated itself, that means there was at least some communication with the GPIB-ENET/1000.
As far as trying to determine what is going on, do you think that your IT people would be willing to help you perform a network capture of the traffic seen at the GPIB-ENET/1000 using Wireshark? This would allow us to see the request going to the box, and see how the box is trying to respond, to see what is going wrong. Hopefully your IT people will already be familiar with this process. The most important detail is that for the capture to work properly, the computer capturing must be connected to the GPIB-ENET/1000 through a hub, instead of a switch, or through a specially configured managed switch which can mirror traffic between two ports.
If you can get Wireshark up and running, I think that it would be sufficient to capture while visiting the ip address in your web browser from the remote subnet.
-Jason S.
