If all of Carl's of suggestions don't resolve the issue, then it is similar to a problem we have experienced.
In our case it is a firewall that does closer packet inspections, sometimes referred to as SPI.
If it is your firewall, then the rules on it have to be tailored, and that is a whole other subject that is going to be specific to the device.
A simple test is to BRIEFLY connect the main computer to the Internet, and see if the installer is able to run. As soon as it passes that stage, I would disconnect it again. There are always risks in bypassing security, so that will be your choice.
As an alternative, if the main computer is a laptop, you can go to a coffee shop with free Internet, and try it there. Again, there are risks, but it is an inexpensive way to try another network setting.
