Why isn the remote Plone server recognizing my username?
If IIS is enabled for NTLM authentication, you must configure Plone to use “Trusted Proxy Authentication”. In this mode, Plone looks at a header sent by EP to determine the username who initiated the request. Although EP will always send this header, it will be ignored by Plone unless Trusted Proxy Authentication is enabled. See the Plone or Enfold Server documentation for more information.