Calculate Date Due Accounting For Holidays

I'm trying to run the code below to add functions to a couple of columns untill the value of the cell is equal to "End". I am recieving the error "Object variable or With block variable not set (Error 91)" and I'm not sure why. I have set my WITH up and I have defined the object. Any thoughts would be greatly appreciated. Thanks.


Option Explicit

Private Sub CommandButton1_Click()
Dim shtXL As Excel.Worksheet
Dim wbkXL As Excel.Workbook

Set shtXL = wbkXL.ActiveSheet
With shtXL
Do Until ActiveCell.Value = "End"

.Range(.Range("W2"), _
.Range("A65536").End(xlUp).Offset(0, 1)).FormulaR1C1 = _
"=Workday(P$2,V:2,Z$2:Z$11)"
.Range(.Range("X2"), _
.Range("A65536").End(xlUp).Offset(0, 1)).FormulaR1C1 = _
"=Workday(S$2,V2)-1"

Loop
End With
End Sub