Error with "this"

This is probably an already answered questions, but you can imagine the trouble using google to find "c# + this".  So I have a class that is trying to trigger an event. 
I have the delegate definition
public delegate void OnServingSelectedEvent(object sender, decimal Serving);
class FractionDecimalTextBox:SourceGrid.Cells.Editors.TextBox
    {
        public event OnServingSelectedEvent OnServingSelected;

        public override bool ApplyEdit()
        {
            OnServingSelected(this, Generals.ToDecimal(Control.Text));
            return base.ApplyEdit();
           
        }
  }

I keep getting the error

Object reference not set to an instance of an object.
With

Cannot obtain value of local or argument '' as it is not available at this instruction pointer, possibly because it has been optimized away.    AutocompleteGrid.FoodGrid.FractionDecimalTextBox

shown in the watch page.
As far as I understand it, this is supposed to point to the current object, but I keep getting this error, although it is completely unregular as I have another class where it works great.  Does anyone know what I am doing wrong?