I have to agree with Graham regarding your choice of text boxes. But if there is some reason you must use what you have then perhaps:
Code:
Sub ScratchMacro()
Dim oShp As Shape
'A basic Word Macro coded by Gregory K. Maxey
On Error Resume Next
For Each oShp In ActiveDocument.Shapes
oShp.TextFrame.TextRange.Text = ""
Next oShp
lbl_Exit:
Exit Sub
End Sub