Disqualifying lead using coding

We are trying to Disqualify lead using code. Code executes fine but lead is not getting disqualified. 

1.Entity DisQualifiedLead = ProjectLeads[0];
2.DisQualifiedLead["statecode"] = new OptionSetValue(2); //Disqualified 
3.DisQualifiedLead["statuscode"] = new OptionSetValue(6); //No Longer Interested"
_orgService.Update(DisQualifiedLead); --> Error - '6 is not a valid status code for state code LeadState.Open on lead 

  4._orgService.Update(DisQualifiedLead);

So if we removed DisQualifiedLead["statuscode"] = new OptionSetValue(6); //No Longer Interested" line, code executes fine but lead is not getting disqualified. 

So question, what is right code for "disqualifying lead" with reason "No Longer Interested"