Can't Add Custom Document Property to Excel File

[bnstout]

I am attempting to add a custom document property to an excel file but am getting a "Invalid Procedure Call or Argument". I am following the same code instructions found in most forums. Can anyone tell me what I am doing wrong?

[ActiveWorkbook.CustomDocumentProperties.Add Name:="Part Number", LinkToContent:=True, Type:=msoPropertyTypeString, Value:=Range("PartNumberMetadata").Value
/CODE]

Please let me know. Thanks!