insert method of Character class failure (error 1004)

[dlb_dlb]

Building an organization diagram. Trying to insert text into each child node.
Program is crashing on insertion of text into the Character object... Here is
a snippet..

Set dgnRoot = shpDiagram.DiagramNode.Children.AddNode

dgnRoot.TextShape.TextFrame.Characters.Insert ("my_string")

I have also pasted the following from the library reference
http://msdn2.microsoft.com/en-us/library/aa224480(office.11).aspx

In the above, the Character.Text property is set, though that too generates
an error as the property is read-only.

Any direction would be appreciated.