Error entering an Array Eneter Formula using VBA

I'm having difficulty entering an array entered formula using vba.

I wrote the formula in the worksheet first using row/column format as per the following

=IFERROR(INDEX(Sheet1!R2C16:R1000C16,MATCH(MAX((Sheet1!R2C16:R1000C16)*(Sheet1!R2C1:R1000C1=Sheet3!RC1)*(Sheet1!R2C3:R1000C3=Sheet3!R1C)),Sheet1!R2C16:R1000C16,0)),"")

The above formula worked great no issues, I then added the following to my sub routine

Dim lr As Long

With Sheets("Sheet3")
    lr = .Range("A" & Rows.Count).End(xlUp).Row
    .Range("B2").FormulaArray = "=IFERROR(INDEX(Sheet1!R2C16:R1000C16,MATCH(MAX((Sheet1!R2C16:R1000C16)*(Sheet1!R2C1:R1000C1=Sheet3!RC1)*(Sheet1!R2C3:R1000C3=Sheet3!R1C)),Sheet1!R2C16:R1000C16,0)),"")"
    .Range("B2").AutoFill.Range ("B2:B" & lr)
End With

I get an error stating "Unable to set FormulaArray property of the Range class" it hangs up on the .FormulaArray line

Any ideas as to what I'm doing wrong.