The parent ticket is not an active ticket (status: closed).
|Reported by:||Owned by:||Mark Ryan|
This is an error displayed when you want to change anything in the child ticket when parent ticket is closed.
This restriction in nonsense and harmful. It prevents from even adding comments to child tickets, when the parent ticket is closed (why????). This is normal trac behaviour to add comments to closed ticket (with some remarks, doing reopen etc). It makes this plugin unusable.
This feature should be removed as unnecessary.