There is no prompt that says "invalid extension" unless you recorded it over some other prompt. There is a prompt that says " I'm sorry that is not a valid entry"
Is the incoming caller dialing an extention number or selecting a menu choice?
From the inside, the person presses the VM button and hears "please enter your password" is this where they get the "invalid" prompt?
If you can clear this up I might have an answer for you.
mark