Barchart Trader tries to disregard custom network settings on the local system, leaving it up to Java to properly route the proxy connections according to the operating systems network connections. If your proxy configuration is specific to the web browser and not Windows in general, Barchart Trader likely will not be able to connect.
PAC within Internet Explorer:
In the case where a PAC file is used within Internet Explorer to configure proxy settings you will need to configure unauthenticated access. Configure this using the IP addresses from http://help.barchart.com/support/solutions/articles/154309-how-do-i-configure-our-firewall-to-work-with-barchart with Port 80 or 443 and without authentication.