Change Password Web Part ERROR

When I add the Change Password web part to a page, it shows up fine if logged in as an admin, but if I log in as a normal user from the external URL, it gives me this error:

"A Membership Provider has not been configured correctly. Check the web.config setttings for this web application"

Here are my provider settings:

enablePasswordRetrieval="false"
enablePasswordReset="true"
requiresQuestionAndAnswer="false"
applicationName="/"
requiresUniqueEmail="true"
passwordFormat="Hashed"
maxInvalidPasswordAttempts="5"
minRequiredPasswordLength="7"
minRequiredNonalphanumericCharacters="1"
passwordAttemptWindow="10"
passwordStrengthRegularExpression=""
My guess is that the external url points to an extended web application - so it has a different web.config than the url where you log in as admin. I'd find both web.configs and compare them - i'm guessing there's an issue with the web.config for your external web app.