Hi GS,
This problem is very difficult to find out. You can check in below ways.
1. Make a group of orders and try to confirm one group at a time. For example if you have 100 orders and want to confirm all; do 10 each time. In that way you will come to know which set of orders is having problem. Its easy to detect.
2. If you find the problem in most of the cases, its better to confirm one by one. There might be issue where you have operation confirmation by mistake and now you are trying to do on header level.
Regards,
Krishnendu.