Problem creating an NT 4.0 trust

I am attempting to create a one way trust between two NT domains. On the PDC for the trusted domain, the admin is going to UserManager for Domains, Policies, Trust relationships, TRUSTING domain area. He is inputting the name of the trusting domain and is inputting an initial password. As soon as he clicks OK, he gets an “access denied” error. He is signed on as administrator for that domain.

What could be causing the access denied message?