Asterisk Connection not working

This is a workaround that I found that is OK for my situation, but I'd generally consider it a gross hack. I found this gem in chan_sip.c:

/* Always OK if no secret */
if (ast_strlen_zero(secret) && ast_strlen_zero(md5secret))
  return AUTH_SUCCESSFUL;

So, my workaround is to put:

secret=

In the config for each extension. This is OK for me because I'm not worried about someone on my network trying to register for an extension that isn't theirs. In general, however, it's totally insecure because it bypasses any further authentication (including my issue with the username mismatch).

That looks like a script error to me, not a settings error. It's reporting that a script is setting __FROM_DID equal to s, not necessarily that the call details from the provider says 's'.

To route different incoming numbers for different purposes, I have extensions.ael with content like:

context incoming-calls {
    441234000000 => {
        Answer();
        Dial(SIP/100,120);
    }

    441234000001 => {
        Answer();
        Dial(SIP/101, 120);
    }
}

Are you using AEL? Do you have incoming call numbers starting 44 instead of 0?