Macro to replace text in column and transfer

Hi, so I was able to fix that aspect of the above code. Thank You. It runs on all worksheets
However I keep getting a runtime error 91 : Object variable or with block variable not set
Wondering how best to fix this

Sub asda()

Dim q As Integer
Dim currentsheet As Worksheet
Dim c As Range, firstaddress As String, a As Long
Worksheets(1).Activate

For q = 1 To ActiveWorkbook.Worksheets.Count
Set currentsheet = ActiveWorkbook.Worksheets(q)
Worksheets(q).Activate


With Columns(1)
  Set c = .Find("Investor", LookIn:=xlValues, LookAt:=xlWhole)
  If Not c Is Nothing Then
    firstaddress = c.Address
    Do
      a = a + 1
      If a > 1 Then c = "Holder"
      c.Offset(, 3) = "% of CSO"
      Range("C" & c.Row & ":C" & c.Row + 20).Value = Range("D" & c.Row & ":D" & c.Row + 20).Value
      Set c = .FindNext(c)
    Loop While Not c Is Nothing And c.Address <> firstaddress
    Range(firstaddress) = "Holder"
    
  End If
End With

Next q

End Sub