503 Error - can't connect

Hi,
Recently mafia has stopped connecting to kol for me. It gives a 503 error. I was hoping someone could help me debug why this is happening. I can connect fine just using chrome.
Below is the debug (which doesn't say much; maybe I need to enable some extra debugging?).
Thanks,
Yvain

Installing default certificate validation...
Validating login server (www.kingdomofloathing.com)...
Server returned response code 503 (Service Unavailable) for login.php
Sending login request...

I can log in to KoL just fine. I'm sure that doesn't help you, but it does let you know that the problem might be personal.

I can barely begin to ask the correct questions, but here are ideas and questions that occur to me.

1. Are you using a brand new build from http://builds.kolmafia.us/?
2. Are you using a Mac or PC?
3. Have you checked if your firewall might be blocking localhost or port 60080?
4. Have you tried downloading KoLmafia to a brand new directory and seeing if you can log in that way?

Thanks for the reply. I was quite baffled. One day it worked fine, the next I start getting 503, and I hadn't changed anything.
Things I've tried:
different/newer version - no success
fresh copy in a different file location - no success
I'm not sure how to check if 127.0.0.1 is blocked, I have no other software which uses it (However I thought 127.0.0.1 would be related to relay browser not login)

I'm on a PC and using a VPN (I'm in china) but had been connecting via the VPN successfully up until recently. I suspect this is to blame but as far as I can see none of its settings have changed. Given that I can login to KoL using a regular browser I suspect its somehow related.
I have Internet Options set to Bypass proxy server for local addresses (previously this has prevented relay browser from working with the VPN but it hadn't prevented me logging in).

And just as oddly (without changing anything) mafia can now connect through my VPN. Maybe I'll just blame it on heightened internet security here over the last week.....

Edit... And it started playing up again the next day.