DUMP:
A new value is to be assigned to the field "<L_BOX>", although this field is entirely or partly protected against changes.
key:
probably you have specified the fields box_tabname and box_fieldname of structure
FORM pf_alv_list_layout USING ps_layout TYPE slis_layout_alv .
CLEAR : ps_layout.
ps_layout-colwidth_optimize = 'X'.
ps_layout-detail_initial_lines = 'X'.
ps_layout-zebra = 'X'.
ps_layout-box_fieldname = 'SEL'."这句的问题
ENDFORM.