Permission required to create a Dot Ras connection

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C#

Hi guys,
Does anyone can help me with this?
I tried to make a new connection using DotRas library,but because of some permission matters in win7,the windows does not allow me to create a entry phonebook.
the code is as follows.
Appreciate for help!

public static void CreateVPNConnection(string connectionName, string serverAddress, string username, string password)
{

            // create vpn connection
            RasDevice device = RasDevice.GetDeviceByName("(L2TP)", RasDeviceType.Vpn, false);
            if (device == null) throw new Exception("Cannot get RasDevice");
            RasEntry entry = RasEntry.CreateVpnEntry(connectionName, serverAddress, RasVpnStrategy.PptpOnly, device);

            // set vpn connection options
            entry.Options.RemoteDefaultGateway = false;
            //entry.Options.IPv6RemoteDefaultGateway = false;
            //entry.Options.ReconnectIfDropped = true;
            entry.Options.ShowDialingProgress = false;
            entry.Options.RequireMSChap2 = true;
            entry.Options.PreviewUserPassword = false;

            // add connection
            RasPhoneBook phoneBook = new RasPhoneBook();
            phoneBook.Open();
            if (phoneBook.Entries.Contains(connectionName))
            {// already exists
                // check if connected
                RasConnection rasConnection = RasConnection.GetActiveConnectionByName(connectionName, phoneBook.Path);
                if (rasConnection != null)
                    rasConnection.HangUp();
                phoneBook.Entries.Remove(connectionName);
            }
            phoneBook.Entries.Add(entry);//You don't have permission               
            // set credentials            
            entry.UpdateCredentials(new System.Net.NetworkCredential(username, password));            
            
            
        }