[Zope] Problem accessing Plone site

Hi everyone, I have problem accessing my Zope/Plone site. I'm on Windows XP pro. Normally, with a fresh ip adress (dynamic ip) I should be able to access my site on my machine or from any others but nothing work. On my machine, I receive an authorization error and on any other, a standard error. Someone know what configuration or parameter I should check to fix my problem? Thanks a lot Etienne