my ASPNet application on IIS Server is using Windows Authentication, anonymous authentication is disabled, Negotiate is in first position for authentication Providers. The users members of the A.D. domain in which the IIS server is joined can login transparently. The users from another approved domain are asked to enter their credentials without success, the credentials popup continuously appears. It seems ISS pool account is not able to validate user's token when they are from an approved domain. Any idea, thanks

Is there a link with delegation authorizations?