define valid sourcing for all ATO model items

 Hi Friends,

I am able to book the sales order, but unable to progress order.Getting note message like "define valid sourcing for all ATO model items" 

Structure of ATO Model : 

 

XYZ Item ----ATO Model

    I

    I

ABC Item----ATO Option Class

                         I 

                         I

                     123 Item---Component Items

                     456 Item---Component Items

I have defined bills for ATO Model and ATO Option Class.

Regards

Chandra....