Disable enter some text to TextItem

 Hi all,

     I have a TextItem and a button A. This button will call LOV when user click on it. Value from Lov assigned to TextItem.

     My goal disable user enter some text to TextItem, they only choice from Lov when they click on button A.

     First, when form start, I configure

          Set_Item_Property('PARAMETERS.MY_TEXTITEM', ENABLED, PROPERTY_FALSE);

     When user click on button and choice value from Lov, I configure:

           Set_Item_Property('PARAMETERS.MY_TEXTITEM', ENABLED, PROPERTY_TRUE);

     After that, I check if MY_TEXTITEM has value , I configure:

           Set_Item_Property('PARAMETERS.MY_TEXTITEM', ENABLED, PROPERTY_FALSE); --->  But I meet error.