IPCop - 1 network cannot surf internet unless proxy is enabled, other network can
 

This is weird, but on one network my users can surf the internet fine without having to specify the IPCop server as their proxy server. IE and Firefox are set to "direct connection to internet".

The other network in another city is set up the same way, however, users cannot surf the internet at all. I have to manually go to each computer and set up their proxy settings in their browser.

Why does it work transparently on one network, yet the other network doesn't work? I've checked the "transparent" option and tried disabling/enabling the proxy server.

I need to be able to have users surf the internet transparently because they will sometimes need to set up their own custom proxy to access web resources in other areas.