Error The hierarchy scheduling structure validation failed after adding child

Hi,

We are getting the error 'The hierarchy scheduling structure validation failed after adding child' for adding parent child relationship with add existing work order.

It is allowing to add existing draft work order with released work order. But it is not allowing to add released work order with another released work order.

Can anyone please let me know, what are the rules will check by system while adding for child work order of existing one.

Thanks,

Narasimhan T