Help with setting chart axes and ranges

I tried the following:

With MyChtObj.Chart.Axes(xlValue, xlPrimary)
        .MinimumScale = "0"
        .MaximumScale = ws.Range("D5").Value
    End With
    

    With MyChtObj.Chart.Axes(xlCategory, xlPrimary)
         .MinimumScale = "0"
         .MaximumScale = ws.Range("D7").Value
    End With

The first part works, i.e. the values are set on the Y axis, but errors out on the highlighted line above?