Verify that permissions are correct for your site's roles, including the generic <em>Anonymous user</em> and <em>Authenticated user</em>. In order to use personal contact forms, users need both <em>View user information</em> (in the <em>User</em> section, which enables them to view user profiles) and <em>Use users' personal contact forms</em> (in the <em>Contact</em> section, which enables them to use contact forms if they can view user profiles).