GetLineReq returning: "Item not valid: The specified line was not found"

Version 1
    This document was generated from CDN thread

    Created by: Laith Abbas on 16-07-2013 11:00:09 AM

    I am trying to use the getLine method with version 9.1. I am giving it a pattern but I keep getting the exception "Item not valid: the specified line was not found"

    I am wondering what am I doing wrong Here is the code that I am trying to execute, I hope that somebody will help.

     public static void callGetLine(AXLAPIService service, string ext)       
          GetLineReq req = new GetLineReq();
          req.ItemsElementName = new ItemsChoiceType55[1];
          req.ItemsElementName[0] = ItemsChoiceType55.pattern;
          req.Items = new object[1];
          req.Items[0] = ext; 
          GetLineRes res = service.getLine(req); 
          GetLineResReturn ret = res.@return;