"Object variable or With block variable not set" in VBA - vba

Question

I am looking to calculate a column (in wsOut) of averages using VBA. The input is in another sheet (wsRefor).
I use the following code, where I use the worksheet function to calculate the average
Dim Avg As Double
Dim AvgRange As Range
Set Reformulering = ActiveSheet
For i = 1 To lastCol
AvgRange = Range(wsRefor.Cells(1 + i, 4), wsRefor.Cells(1 + i, lastCol))
wsOut.Cells(i + 1, 4).Value = Application.WorksheetFunction.Average(AvgRange)
Next
Yet, I get the mistake, from the second line inside of the for-loop:
"Object variable or With block variable not set"
I am not sure I understand the error from videos I have watched and other forum discussion, so I am hoping anyone can explain or potentially point of the mistake

Answer 1

You need to use the Set keyword when you are assigning an object rather than a value.
A Range is an object and so it needs to be Set
Set AvgRange = Range(wsRefor.Cells(1 + i, 4), wsRefor.Cells(1 + i, lastCol))
To see the difference, you can do this:
Dim test As Variant
Range("A1").Value = "some text"
test = Range("A1") '// test is now a string containing "some text"
Set test = Range("A1") '// test is now a range object
MsgBox test.Value '// Displays the value of the range object "some text"

Answer 2

Assuming you defined Dim wsRefor As Worksheet, and set it to the right Sheet, then modify your line:
AvgRange = Range(wsRefor.Cells(1 + i, 4), wsRefor.Cells(1 + i, lastCol))
to:
Set AvgRange = wsRefor.Range(Cells(1 + i, 4), Cells(1 + i, lastCol))
or, on the safe side:
With wsRefor
Set AvgRange = .Range(.Cells(1 + i, 4), .Cells(1 + i, lastCol))
End With
Edit 1: full code which I've tested (also has error handling for the Average Function)
Option Explicit
Sub DynamicAvgRange()
Dim wsRefor As Worksheet
Dim wsOut As Worksheet
Dim Avg As Double
Dim AvgRange As Range
Dim lastCol As Long
Dim i As Long
Set wsRefor = ThisWorkbook.Sheets("Refor")
Set wsOut = ThisWorkbook.Sheets("Out")
' just for simulating the tests
lastCol = 6
For i = 1 To lastCol
With wsRefor
Set AvgRange = .Range(.Cells(1 + i, 4), .Cells(1 + i, lastCol))
End With
If Not IsError(Application.Average(AvgRange)) Then
wsOut.Cells(i + 1, 4).Value = Application.Average(AvgRange)
Else
' Average value returned an error (no values in the searched range)
wsOut.Cells(i + 1, 4).Value = "" ' put a blank value >> modify to your needs
End If
Next i
End Sub