Determing security demand for ServiceDescriptionImporter()

I'm trying to create an instance of
System.Web.Services.Description.ServiceDescriptionImporter (in .Net 1.1) in
an assembly that refuses all permissions and then requests the individual
ones it needs. Problem is, when I do this, I get a security demand as soon
as I call the method that contains a call to the constructor for
ServiceDescriptionImporter. When I look in the exception, the RefusedSet
property is null, so I have no idea which permission it needs. Only one I
see in the constructor for it are the ones to call Activator.CreateInstance,
and there are no documented permissions for either the 1.1 or 2.0 version of
the class.
Anyone know what permissions the ctor needs or how I can get an exception
that actually shows the refused permissionset?