The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request POST /login/.
Reason: Error reading from remote server
and even installing and trying the TorBrowser (to circumvent any proxies - never had trouble with that elsewhere from these computers), I finally got a different message when trying to use the same e-mail/pass combination in the "play" link instead, which prompted me that the problem might be that the @ character that I had used in the passwords was not correctly interpreted.
As soon as I tried yet another e-mail adress with a password that doesn't contain the @ character, everything worked flawlessly (at this point I had a character going already and absolutely needed web access for the Grid). The trouble can still be reproduced (that's how I could copy/paste the error message now even though I can finally use the forums as well).
- don't use an @ in your web password for now
- this is also a bug report for the webmaster to look into that problem
Finally, I am glad to have been that persistent despite the troubles, because the game seems great.