In forms on Do_key('List_values')

I have a text item which is associated to a LOV and in the trigger Key_Listval I wrote the code to handle the LOV. But the problem is I have a button on the same canvas and block for the When-Button-Pressed trigger I wrote
Do_key('List_Values'); but instead of raising the trigger I am getting an error "Field Doesnot Understand Operation". Why is it happening. It is happening when the cursor is in the text item I am pressing the button.

Any help is greatly apprciated.