I have a similar problem, the GUI does load, just loads up blank (100% apparently!)
I'm away from my Pi for the weekend however when I'm back at school on Monday I will give
sudo chmod -R 775 /var/lib/indiecity/pistore
a shot as suggested. I too run through a school proxy. I have edited the /etc/bash.bashrc with the following 3 commands,
as the school uses smoothwall I am channelling all data through port 9090, not sure if this might be an issue. Also not sure if I need the 'export https_proxy' command but I'll leave it. A note to fellow teachers, don't try using a smoothwall.proxy.local the Pi just ignores it, find the IP Address and go with that!
I will update post tests.
Thanks for keeping this forum active.