I cannot get past an "unknown problem" error when trying to login to discussions.apple.com
There are occasional timeouts when the service that validates an Apple ID and password combination fails to report back to the web server running any of Apple's services (like the discussions, stores, review process, bug reporter, etc...)

If this error persists over a day or more and there isn't a public outage, you will need to contact support for help with your Apple ID.