Must not maintain bill of materials without assigned change number

Hi  all experts !    i need help.

The master data  in customer site , is maintained  mandatory with assigned change number.

For bill of material creation

1. Creation of change number   ( CC01N )
2. Execute CS01   and assigned the change number , populate all the required field and save

For bill of material maintenance

1. Creation of change number   ( CC01N )
2. Execute CS02   and assigned the change number , populate all the required field and save

( The system must block   and display error message if any user is trying to create or maintain bill of materials without assigned  change number )

That is the  required processing for master data maintenance.  However, i had a critical issue  today because  user are   able to maintain bill of material without assigned chagne number.

Please help me to find the solution.

Thanks