Need some help with table views...

My first question is in regards to customizing headers in a table view. The problem I'm having is that when I declare GetViewForHeader, it's overwriting the header names (or erasing them) I'm generating from TitleForHeader. Here are the two methods:

public override UIView GetViewForHeader (UITableView tableView, int section)
{
  UILabel headerLabel = new UILabel ();
  headerLabel.TextColor = UIColor.Black;
  headerLabel.Font = UIFont.BoldSystemFontOfSize (18.0f);
  headerLabel.Frame = new RectangleF (15.0f, 0.0f, 500.0f, 20.0f);

  return headerLabel;
}

public override string TitleForHeader (UITableView tableView, int section)
{
  return data [section].QuestionName;
}

My second question relates to multiple selections within a table view. I currently have a table that is grouped into various sections, and I want to be able to select an item from each section, but only one item per section (similar behavior to a radio button I guess). I've set AllowMultipleSelections = true, which of course allows me to select multiple rows in each section which is not what I'm going for. I tried this code but received a null reference exception:

public override NSIndexPath WillSelectRow (UITableView tableView, NSIndexPath indexPath)
{
  foreach (var selectedIndex in tableView.IndexPathsForSelectedRows) 
  {
    if (selectedIndex.Section == indexPath.Section) 
        tableView.DeselectRow (selectedIndex, false);
  }

  return indexPath;

}

I don't even think this is probably the best or most efficient way to approach this so any help or guidance would be much appreciated. Thank you.