Hi Rahul,
i think the reference context node is not initialized so do one thing.
first check view is in display mode or not any wise that is in display mode so read the context node and then turn that nodes into editable.
ex:
view_group_context->is_view_in_display_mode( me ) EQ abap_false.
lr_vgc ?= view_group_context->get_dependant_vg_context( ).
lr_vgc->set_all_editable( ).
see this link you can understand easily.
Overview page toggle Display -Edit - Display
Regards,
Srinivas.