You're trying to access an older version of Mgmt API, which was
deprecated in Aug 2011 and was turned off recently. Since August, we
have sent out a number of reminders that XML requests for the older
versions will automatically receive v2.4 responses, and that
older JSON response, which is no longer supported. We have added a
completely new JSON output in version 3.0 and it supports new JS
client libraries as well. We would recommend that you start using the
newer version of the API -- either v2.4 (XML) or v3.0 (JSON).