activesheet.tab.colorindex not working when workbook shared
 

I have a workbook with the following code operating correctly in exclusive access. However, this code fails with an error 1004 when the workbook is put into shared mode. This will fail for a single cell named as "PassFail"

Any thoughts?

For Each C In Range("PassFail")
If C.Value = "Fail" Then
ActiveSheet.Tab.ColorIndex = 3
ElseIf C.Value = "Pass" Then
ActiveSheet.Tab.ColorIndex = 4
End If
Next c