Cheikh:
You will need to add that parameter. Under Scheme Settings > Fields: click the downward pointing arrow next to "Add" and select Add Object Parameters. Find the Object (Lamp) you are using and you will see its parameters under Available Parameters. In this case I think the parameter you want is near the bottom of the list: Variable = txt, Type = abc, Name = Text (I had to guess to find this, but it was near the "Text in 2D" Name). Click ">>Add>>" after finding the desired parameter, and it will show up in the Schedule Fields.
David