Some people may feel an error statement like that is indiscriminate use of brute force.
Another way to handle that issue is check to ensure the CC is not showing placeholder text.
While it probably doesn't matter in your case, if you had a shape or something anchored in the a rich text control that code my delete the shape.
You could also try:
Code:
Private Sub Document_ContentControlOnExit(ByVal CCtrl As ContentControl, Cancel As Boolean)
With CCtrl
Select Case .Type
Case wdContentControlText, wdContentControlRichText, wdContentControlComboBox
If Not CCtrl.ShowingPlaceholderText Then
.Range.Case = wdTitleSentence
End If
Case Else
End Select
End With
End Sub