Object reference not set to an instance of an object.

private void LoadHeaders()
   {




       for (int index = 1; index <= NO_OF_HEADERS_TO_DISPLAY; index++)
       {

           var uiUploadHeader = FindControl(string.Format("uiUploadHeaderImage{0}", index)) as Admin_Controls_Upload;
           var uiTxtHeaderText = FindControl(string.Format("uiTxtHeaderText{0}", index)) as TextBox;

           var uiHidHeaderID = FindControl(string.Format("uiHidHeaderID{0}", index)) as HiddenField;

           WebSiteHeader header;
           bool isNewHeader = false,
                   headerUploaded = false;
           int headerID;

           int.TryParse(uiHidHeaderID.Value, out headerID);
           if (headerID > 0)
           {
               header = Webcoda.Cms.DAL.Context.Instance.WebSiteHeaders.Where(o => o.ID == headerID).SingleOrDefault();
           }
           else
           {
               isNewHeader = true;
               header = new WebSiteHeader();


           }

           if (index > 1)
           {
               // Delete header
               if (uiUploadHeader.DeleteCurrentFile && !isNewHeader)
               {
                   uiUploadHeader.DeleteImage(string.Format("{0}{1}", this.DataSource.HeaderImagesPath, header.HeaderImageSrc));
                   Webcoda.Cms.DAL.Context.Instance.WebSiteHeaders.DeleteOnSubmit(header);
                   return;
               }

               //  Update / Create  header



               string headerImageName;
               uiUploadHeader.Fill(this.DataSource.HeaderImagesPath, string.Format("{0}_{1}", this.HEADER_IMAGE_DEFAULT, index), true, true, out headerImageName);
               if (!string.IsNullOrEmpty(headerImageName))
               {
                   headerUploaded = true;
                   header.HeaderImageSrc = headerImageName;
               }
               else
               {

               }

           }
           else
           {
               headerUploaded = true;
               header.HeaderImageSrc = this.DataSource.WebSiteStyles[0].HeaderImageSrc;
           }
           header.HeaderImageText = uiTxtHeaderText.Text;

           if (isNewHeader && headerUploaded)
           {
               this.DataSource.WebSiteHeaders.Add(header);
           }

       }
   }

string headerImageName;
               uiUploadHeader.Fill(this.DataSource.HeaderImagesPath, string.Format("{0}_{1}", this.HEADER_IMAGE_DEFAULT, index), true, true, out headerImageName);
               if (!string.IsNullOrEmpty(headerImageName))
               {
                   headerUploaded = true;
                   header.HeaderImageSrc = headerImageName; //619th line
               }
               else
               {

               }