Saving Workbook as xlsx

Hi all,

I have the following code but it's errors (1004), stating an invalid extension. I'm trying to save the Active Workbook in a different location as a XLSX file. Any ideas?

Dim myFileName$
   myFileName = ThisWorkbook.Name
   ActiveWorkbook.SaveAs "C:\Users\MyName\Desktop\Replicated\" & myFileName, FileFormat:=51
   ActiveWorkbook.Save