Apply LEFT & RIGHT function to column

Hi all,

I have the following code, which is supposed to combine the values from column I and column AD:

Sub Pro1()

Sheets("GR4").Select
Columns("AF:AF").Select
Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFormatFromLeftOrAbove

    Dim lastRow As Long
    lastRow = Cells(rows.Count, "AD").End(xlUp).Row

    Columns("AF:AF").Select
    Selection.NumberFormat = "General"

    Range("AF2:AF" & lastRow).FormulaR1C1 = "=right(AD2,10)&left(I2,14)"
    
    Range("AF2").CurrentRegion.Select


End Sub

When running the code it works, but I get a #NAME error in the worksheet, and the formula appears in column AF as =right('AD2',10)&left('I2',14) with the ' ' around the cell references

Any ideas why?