Set Shape as Another Shape Fails.. ??

The following code fails:

Function Shapes_Exist(WS As Worksheet, ShapeName As String) As Boolean
' does the shape with the ShapeName name exist?
Dim tmpID As Long

  On Error Resume Next
  Shapes_Exist = False
  tmpID = WS.Shapes(ShapeName).Id
  If IsEmpty(tmpID) Then
    Shapes_Exist = False
  Else
    Shapes_Exist = True
  End If
  On Error GoTo 0

End Function
	
	
TempBool = Shapes_Exist(BWS, GroupName)
If TempBool = True Then
	DupeFound = True
	Set pShape = BWS.Shapes(GroupName)
End If

gives the following error:
Run-Time error '-2147024809 (80070057)':
The item with the specified name wasn't found

the shape with the name "GroupName" does not exist, but my function returns true that it does exist. Not sure why. Please help. Thanks.