Why is HttpContext.Current.Profile NULL? How does it get a value?

I inherited MOSS code which implements a custom profile provider. The setup seems to be okay (provider & web.config).
A user can login, however, after logging in, the HttpContext.Current.Profile object is null. Why is it null? How/When is is supposed to get a value?
HttpContext.Current.User.Identity.Name has a value after loggin in.
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