Left function in a Select Case Macro

I am trying to put together a Select Case macro and am having problems with the Left function on the first line. If i don't have it there the macro works fine. Does anyone have any ideas?

Sub Macro1()

  CurrentSelectedCell = ActiveCell.Row

   Select Case Left(Cells(CurrentSelectedCell, 1), 6).Value & " " & Cells(CurrentSelectedCell, 2).Value & " " & Cells(CurrentSelectedCell, 3).Value
        Case "542851 Loadsa AirMiles"
            Cells(CurrentSelectedCell, 4) = "FSA"
        Case "542852 Loadsa AirMiles"
            Cells(CurrentSelectedCell, 4) = "FSA2"
        Case "542851 Many Many 3rd Party Error"
            Cells(CurrentSelectedCell, 4) = "IPA"
            
        Case Else
            Cells(CurrentSelectedCell, 4) = ""
      End Select
End Sub

Many Thanks