Optimize code

If file is saved as .xlsm then yes you must change this. If it is file with code we may use better syntax:

Sub ImportPCB()
'
' ImportPCB Macro
'

'
   Const csPATH                    As String = "C:\Users\allaer81\Documents\Dimitri04Feb2014\"
   
   ' change this number as required
   Const NUMBER_OF_FILES           As Long = 11
   
   Dim wb                          As Workbook
   Dim n                           As Long

   Application.ScreenUpdating = False

   Set wb = Workbooks.Open(Filename:=csPATH & "PCBS01.CSV")
   wb.Sheets(1).Columns("A:B").Copy
   ThisWorkbook.ActiveSheet.Range("A1").PasteSpecial Paste:=xlPasteValues, _
                                                                       Operation:=xlNone, SkipBlanks:=False, Transpose:=False
   Application.CutCopyMode = False
   wb.Close False

   For n = 2 To NUMBER_OF_FILES

      Set wb = Workbooks.Open(Filename:=csPATH & "PCBS" & Format(n, "00") & ".CSV")
      wb.Sheets(1).Columns("B:B").Copy Destination:=ThisWorkbook.ActiveSheet.Cells(1, n + 1)
      wb.Close False
   Next n

   Cells.NumberFormat = "0.00"

   Range("B2").Value = "PCBS01"
   Range("B2").AutoFill Destination:=Range("B2:L2"), Type:=xlFillDefault
   Cells(2, NUMBER_OF_FILES + 2).Resize(, 3).Value = Array("Average", "STDEV", "%")
   Cells(4, NUMBER_OF_FILES + 2).FormulaR1C1 = "=AVERAGE(RC[-11]:RC[-1])"
   Cells(4, NUMBER_OF_FILES + 3).FormulaR1C1 = "=STDEV(RC[-12]:RC[-2])"
   With Cells(4, NUMBER_OF_FILES + 4)
      .FormulaR1C1 = "=RC[-1]/RC[-2]"
      .NumberFormat = "0.0000%"
   End With
   Cells(4, NUMBER_OF_FILES + 2).Resize(, 3).AutoFill Destination:=Cells(4, NUMBER_OF_FILES + 2).Resize(200, 3)


   Cells.EntireColumn.AutoFit
   
   Application.ScreenUpdating = True

End Sub