Regarding Back Button

Hi,

I have created one module pool program which has screen no's 100, 200 300. I have one docking container on the main screen i.e. screen 100. When i go to screen 200 and click Back button i am not getting the docking container.

I tried these two codes.

CASE SY-UCOMM.

WHEN 'BACK'.

SET SCREEN 100.

ENDCASE.

********************

Case SY-UCOMM.

WHEN 'BACK'.

CALL SCREEN 100.

ENDCASE.

Both are not working. Can anyone help