Craig,

>I have a form with a project list on it, from here a sub-form can be opened for editing some of the details.
>
>If details are changed and saved in the sub form, how do I notify the original form of changes?
>
>Currently both the parent and child forms have their own copy of the business object registered. I pass in the ID required to the child form.
>
>Is it perhaps better (in this case) to pass in the currently referenced entity from the parent form instead, or is there a better way?

Depending on what you're trying to accomplish you can do it either way. If they are editing the same data, I recommend passing a reference to the other form. You can still register the business object. For example:

public ChildForm(Inventory inventory)
{
   this.oInventory = this.RegisterBizObj(inventory);
}

Best Regards,