Excel CalCulation Issue

[C.R.]

SamT,

Where: File>>>Options>>>Formulas>>> Workbook Calculation>>> Automatic Radio Button is selected.

How: In a ThisWorkBook Module (From The Tips and Tricks Sticky)

Private Sub Workbook_Open()
    Application.OnTime Now, "ContinueOpen"
End Sub

"ContinueOpen" is:

Sub RestoreSheetsCalculation()
  Dim sh As Worksheet
  For Each sh In Worksheets
    sh.EnableCalculation = True
  Next
  Application.EnableEvents = True
  Application.Calculation = xlCalculationAutomatic
MsgBox "Auto-Calculation Enabled."
End Sub

I've checked all the other Modules and there isn't anything that would disable Automatic Calculation.
This is what's weird here. It is an intermittent problem with a workbook that gets used, by me only, on a daily basis.

Thanks for your help.

C.R.