Makro klappt nicht mehr - Für Fehlerfindige!

Sub Wilson()
Dim i As Integer
Dim u As Integer
Dim ze As Double
Dim a As Double
Dim b As Double
Dim sqrt As Double
'LOK einfärben
For i = 6 To 73
b = Cells(i, 5)
a = Cells(i, 4)
If Left(a, 1) = "K" Then
If a  0 Then
sqrt = (b * (a - b) / a + 1 / 4) ^ (0.5)
ze = (b + 1 / 2) / (a + 1) + (1 / (a + 1)) * sqrt
If ze >= 0.9 Then
Cells(i, 6).Interior.ColorIndex = 4
ElseIf ze >= 0.8 And ze = 0.6 And ze  0 And ze  0 Then
sqrt = (b * (a - b) / a + 1 / 4) ^ (0.5)
ze = (b + 1 / 2) / (a + 1) + (1 / (a + 1)) * sqrt
If ze >= 0.9 Then
Cells(i, 9).Interior.ColorIndex = 4
ElseIf ze >= 0.8 And ze = 0.6 And ze  0 And ze  0 Then
sqrt = (b * (a - b) / a + 1 / 4) ^ (0.5)
ze = (b + 1 / 2) / (a + 1) + (1 / (a + 1)) * sqrt
If ze >= 0.9 Then
Cells(i, 12).Interior.ColorIndex = 4
ElseIf ze >= 0.8 And ze = 0.6 And ze  0 And ze