I was unfamiliar with the credentials() function, and had always grabbed the get_basic_credentials() call to do my stuff - blame it on my not reading carefully. :-/

I have had that type of an error (I won't say exact, because I don't remember it exactly) happen when no_proxy wasn't working the way that I thought, and an internal site was hitting the outside proxy. Since the outer proxy didn't recognize the internal username and password, and could not have even connected to the internal server, I was hosed from the start.

I seem to remember there being a way to force verbose output, and using that to find out what was actually happening.