Just to add to this...
minor changes to the variant/orders did allow processing of the orders.
Ex.
1. Remove a shipping point from the variant
2. change the shipping condition in the STO etc.
Though it works for once , next time similar changes do not work.
I doubt there is breakage in the delivery due list program due to the support packs but looking for some expert advice before I raise this with SAP.
Regards,
Deb