error checking inside nested loop

[knacksc2]

Well, i am sure this looks silly, but why wouldn't this error checking method work when both cells are blank?

Sub Populate_Data()


Sheet3.Select
Dim a As Integer
a = Application.WorksheetFunction.CountA(Sheet3.Range(Cells(7, 1), Cells(1040000, 1)))


Sheet2.Select
For b = 1 To a


For c = 1 To 13


Sheet3.Cells(6 + b, (c * 7) - 5).Value = Application.WorksheetFunction.VLookup(Sheet3.Cells(6 + b, 1).Value, Sheet2.Range(Cells(7, 1), Cells(6 + a, 14)), c + 1, False)
Sheet3.Cells(6 + b, (c * 7) - 4).Value = Application.WorksheetFunction.VLookup(Sheet3.Cells(6 + b, 1).Value, Sheet2.Range(Cells(267, 1), Cells(266 + a, 14)), c + 1, False)


Dim var000 'check if there is an error in calculating hit rate
    var000 = Sheet3.Cells(6 + b, (c * 7) - 4).Value / Sheet3.Cells(6 + b, (c * 7) - 5).Value
    Dim iserr000 As Boolean
    iserr000 = IsError(var000)
    If iserr000 = True Then
    Sheet3.Cells(6 + b, (c * 7) - 3).Value = ""
    Else
    Sheet3.Cells(6 + b, (c * 7) - 3).Value = Sheet3.Cells(6 + b, (c * 7) - 4).Value / Sheet3.Cells(6 + b, (c * 7) - 5).Value
    End If


Next c
Next b


End Sub