解决ASP.NET创建的线程的用户改变引发的拒绝访问错误

 asp.net创建的线程的用户由<identity impersonate="true"/> 改为nt authoritynetwork service, 引起"system.unauthorizedaccessexception","拒绝访问"

    dim thr as threading.thread
    dim l as system.security.principal.windowsidentity

    function print()
        thr = new threading.thread(addressof printautocad)
        thr.start()
        l = system.security.principal.windowsidentity.getcurrent
    end function

    private sub printautocad()
        system.security.principal.windowsidentity.impersonate(l.token)
 ...
    end function