SUMIFS Test on multiple lastrows

Hi Gurus and Experts,

I have been playing with the SUMIFS formula code for a while now but I am not sure why it is still showing the error. I have written the following code:

Sub A()

Dim endrow as Long, lastrow as Long

 '........ endrow, lrow and lastrow are set in different stages of processing

For i = endrow To 1 Step -1
    If ActiveSheet.Range("C" & i).Value = "Table Head" Then
        ActiveSheet.Range("C" & i + 1).Formula "=SUMIFS(R[-" & lastrow + 20 - 1 & "]C[18]:R[-23]C[18]," & _
        "R[-" & lastrow + 20 - 1 & "]C:R[-23]C,""AA"")"
        Exit For
    End If
Next I

End Sub

For reference, I am attaching the excel file herewith. It would be of immense help if I could get the guidance to trace where I committed mistakes.

Thank you
Roshan Shakya