Unable To Run Script From Return Key

I'm using the code below to track changes in a Excel worksheet.

Code:
Option Explicit

Public preValue As Variant
Private Sub Worksheet_Change(ByVal Target As Range)

Dim cell As Range
Dim Rng As Range
Dim Rng2 As Range
Dim Rng3 As Range

Application.EnableCancelKey = xlDisabled

[Code] ........

The code works fine, except for this piece of the script:

Code:
If Target.Column = 50 Then

If Target.Value = "Yes" Then
Set Rng = Application.Union(Cells(ActiveCell.Row, "B").Resize(, 22), Cells(ActiveCell.Row, "W"))
Rng.Interior.ColorIndex = xlNone
Set Rng2 = Application.Union(Cells(ActiveCell.Row, "X").Resize(, 12), Cells(ActiveCell.Row, "AI"))

[Code] .........

If I add the word "Yes" to column "AX (column 50) and press the Return key, the above code i.e. the change of fill colour, doesn't work.

If however I enter the word "Yes" and select another cell by clicking in it, the code works.