ошибка "Run-time error '91': Object variable or With block variable not set"

    Dim rng As Range
    Set rng = Range("AK5:AK68").Find(n)
    If rng Is Nothing Then
        MsgBox "Çíà÷åíèå " & n & " íå íàéäåíî â äèàïàçîíå AK5:AK68."
        End
    Else
        rng.Activate
        i = rng.Row
    End If

Range("AK5:AK68").Find(n, LookIn:=xlValues)

Function Find(R As Range, V) As Range
    For Each c In R
        If c.Value = V Then
            Set Find = c
            Exit Function
        End If
    Next
End Function

Range("AK5:AK68").Find(n)
 на 
Find(Range("AK5:AK68"),n)
или
Find([AK5:AK68],n)

Public Function ...

Sub Main1()
    Dim i As Long, x As Range, Fst As String
    Application.ScreenUpdating = False
    Workbooks("ОРМ.xls").Sheets(1).Activate
    With Workbooks("ОРМск.xls").Sheets(1)
        Columns("G").Interior.ColorIndex = xlNone
        .Columns("G").Interior.ColorIndex = xlNone
        For i = 1 To Cells(Rows.Count, "G").End(xlUp).Row
            Set x = .Columns("G").Find(what:=Cells(i, "G"), LookAt:=xlWhole)
            If Not x Is Nothing Then
                Cells(i, "G").Interior.ColorIndex = 6
                Fst = x.Address
                Do
                    .Cells(x.Row, "G").Interior.ColorIndex = 6
                    Set x = .Columns("G").FindNext(x)
                Loop While Fst <> x.Address 'выделенная в коде строка
            End If
        Next
    End With
End Sub