Change Windows Password - error 5

I have installed the IIS feature to change your windows password when it
expires when you log on to OWA. Now this function works fine when we have
our warehouse personnel open OWA while on our network. But, if we have
office personnel traveling and their password expires they get the IIS
change password screen only when they enter the new password the response
they get is Error 5. Can anyone tell me what this error is and how to
correct it so this function works?