PrincipalPermission, getting started

[codefragment@googlemail.com]

Hi
On a machine called 'machineName', a user called userName is a
member of the ora_dba group. I can see this in computer management.
Why then does the below throw an exception?


AppDomain.Curre ntDomain.SetPri ncipalPolicy(Pr incipalPolicy.W indowsPrincipal );

PrincipalPermis sion p = new PrincipalPermis sion("\\machine Name
\userName", @"machineName\o ra_dba", true);
p.Demand();

thanks