how to clear parameters defined in selection screen on back button

Hi,

I have a report with parameters, few being input fields, and check boxes. After report is executed when user selects the back button, the selection screen is displayed again but with the old selection values. I want to clear them.

So in the Initialization even I added the code to clear all these parameters;

CLEAR: p_aaa, p_bbb, p_ccc.

I debugged and control passes through this code but still the fields are not cleared and they retain the old input values.

How to clear them ?

thnks