[SalesForce] Web Service Callout exception: Invalid Session Id

public class webServicesTriggerClass
{
  @future(callout = true)
   public static void webServicesMethod(list<ID> Id1)
   {   
   partnerSoapSforceCom.Soap sp = new partnerSoapSforceCom.Soap(); 
   partnerSoapSforceCom.LoginResult lr = sp.login('****','****');
   soapSforceComSchemasClassNiralaapp.SessionHeader_element ses = new soapSforceComSchemasClassNiralaapp.SessionHeader_element();
    system.debug('################################' +ses.sessionId);
    ses.sessionId = lr.sessionId; 
   system.debug('################################' +ses.sessionId);   
   soapSforceComSchemasClassNiralaapp.MyFriendsDetailSoapApi vNapp=new soapSforceComSchemasClassNiralaapp.MyFriendsDetailSoapApi();
   list<MyFriend__c> mfList=new list<MyFriend__c>([select id,myEmail__c,friendName__c,friendEmail__c,aboutFriend__c ,age__c from MyFriend__c where id in:id1]);
     for(MyFriend__c mf:mfList)
      {
     string  s1= mf.myEmail__c;
     string  s2=mf.friendName__c;
     string  s3=mf.friendEmail__c;
     string  s4=mf.aboutFriend__c;
     integer i1=Integer.ValueOf(mf.age__c);
     boolean result=vNapp.addFriendDetails(s1,s2,s3,s4,i1);
     system.debug('################################' +result);    
      }
   }
}

Trigger–

trigger webServicesTrigger on MyFriend__c (after insert) 
 {
    list<ID> Ids=new list<ID>();
    for(MyFriend__c mYFR:Trigger.new)
     {
       Ids.add(mYFR.Id);
     }
     webServicesTriggerClass.webServicesMethod(Ids);
 }

When I am executing this code, I am getting this error-

System.CalloutException: Web service callout failed: WebService
returned a SOAP Fault: INVALID_SESSION_ID: Invalid Session ID found in
SessionHeader: Illegal Session faultcode=sf:INVALID_SESSION_ID
faultactor=