I can't delete a group

Good morning,
I try to delete a group in this way:
groupParent.Delete(groupChild), but this return false.

groupChild is empty:
groupChild.ObjDefList(true).length=0
groupChild.ModelList(true).length=0
groupChild.Childs(true).length=0

but groupParent.Delete(groupChild)=false

I see that groupChild.ObjDefList().length=1 so I checked if groupChild was locked:
var reportcomponent = Context.getComponent("Locking");
reportcomponent.getLockInfo(groupChild.ObjDefList()[0]) but is getLockState is UNLOCKED.

How I can delete the groupChild?
Thanks and best regards