Whats wrong with this code??

'Revise Account Name

Range("Y1").Select
LastRow = Range("A65536").End(xlUp).Row
ActiveCell.FormulaR1C1 = "=+RC[-22]&' - '&RC[-20]"
Selection.AutoFill Destination:=Range("Y2:Y" & LastRow), Type:=xlFillDefault
Range("Y1").Select
ActiveCell.FormulaR1C1 = "AccountName"
Range("A1").Select

The code trips up on (ActiveCell.FormulaR1C1 = "=+RC[-22]&' - '&RC[-20]")