Field symbol syntax for SAP_APPL 605

Hi

I am on SAP_APPL 605, trying to convert columns into rows with field symbols..though having no syntax errors in code it is thorwing dump.

Below is my sample code :

Looping table (it_grp_display_tmp) has 2 columns :

1.  Column mrgamt  has     12 records which I want to convert it into row 1 with type GPRVAL, with rowtxt-field as 'Amount'

2.  Column Netwr    has     12 records which I want to convert it into row 2 with type GPRVAL  with rowtxt-field as 'Margin'

So I am trying to convert 1st column into row, but with no syntax error it is giving dump & debugger sy-subrc is 4.

Is there is something missing in code or I have to use different syntax because of older version. ???

Please guide me to field-symbol syntax link for 605 or correct me if I missing some logic ...