I'm not certain why this would matter for proxy configurations, but you may want to try changing your initial context factory and protocol values. These were deprecated and replaced. The preferred values now are:
Initial Context Factory:
Since the proxy settings are Java system values, it doesn't seem like it should matter -- the underlying connection should pick up on the Java system settings. It's worth a shot, though.
Edit: I also just noticed that you are using both the setting to use system proxies (as configured in internet explorer), and also trying to manually set the proxy values. I don't know which takes precedence. Have you tried to remove the "java.net.useSystemProxies" property, or setting it to false?