sorry for my stupid question but i've got the same problem but i don't have an sip compliance router (zyxel p652hw). i can't register myself to my voip provider (wengo) and i've got the same error as you.
everything work fine with fring with the same parameters that i've entered into my e65 sip phone.
my stupid question is : do i need to have a sip compliance router to connect directly from my e65 to my voip operator ?
thanks for your help,