Hi there,
Thanks for coming to my aid on this one! It was really just a human blunder....
I was connected to the device with a statically addressed LAN port on a laptop. Meanwhile the laptop was connected to our enterprise network via wireless, so I could remote into my laptop and work on the juniper from my main machine. The device didn't mind responding to ping or allow SSH while I worked in this manner.
When I turned the wireless function off on the laptop and removed the proxy settings the GUI worked fine. Its always the basic things.