VBA for pivot table won't group fields

My macro creates a pivot table but I am running into an issue when it goes to group one of the numeric columns as I get a "Group method of Range class failed" message. The grouping portion of the code is from a recorder. The rest of the code not shown attempts to group three other fields and then finish out. Any thoughts on how to fix this?

Also, I have to create this report weekly so it's a new one each week. Do you see any code issues with the creation of the table? I've noticed that the pivot table # changes each time it gets created so I'm wondering if I need to be more exact? Sorry if that second question is too vague. Thanks!

Pivot table
Dim PTCache As PivotCache
Dim PT As PivotTable

Set PTCache = ActiveWorkbook.PivotCaches.Create(SourceType:=xlDatabase, SourceData:=Range("A1").CurrentRegion)

'Adding new sheet for the pivot table
Worksheets.Add

'Creating the Pivot Table
Set PT = ActiveSheet.PivotTables.Add(PivotCache:=PTCache, TableDestination:=Range("A3"))


 ActiveSheet.PivotTables("PivotTable1").RowAxisLayout xlTabularRow
    With ActiveSheet.PivotTables("PivotTable1")
        .ColumnGrand = False
        .RowGrand = False
    End With
    With ActiveSheet.PivotTables("PivotTable1").PivotFields("Grade 1")
        .Orientation = xlRowField
        .Position = 1
    End With
        
    Selection.Group Start:=True, End:=100, By:=15
    ActiveSheet.PivotTables("PivotTable1").PivotFields("Grade 1").Orientation = _
        xlHidden

I was able to figure this out. Here is the code.

Sub WeeklyReportStep8()
'Pivot Table creation

Dim PTCache As PivotCache
Dim PT As PivotTable
Dim PF As PivotField


'Create the Cache
Set PTCache = ActiveWorkbook.PivotCaches.Create( _
    SourceType:=xlDatabase, _
    SourceData:=Range("A1").CurrentRegion)
    
'Add a new sheet for the pivot table
Worksheets.Add

Application.ScreenUpdating = False

'Create the pivot table
Set PT = ActiveSheet.PivotTables.Add( _
    PivotCache:=PTCache, _
    TableDestination:=Range("A3"))

PT.RowAxisLayout xlTabularRow
PT.ShowDrillIndicators = False
PT.ColumnGrand = False
PT.RowGrand = False


'specify fields to be grouped
With PT
    .PivotFields("Grade 1").Orientation = xlRowField
End With

Dim rPTRange As Range
Set PF = PT.RowFields("Grade 1")
Set rPTRange = PF.DataRange.Cells(1, 1)
rPTRange.Group Start:=True, End:=100, By:=15

With PT
    .PivotFields("Grade 1").Orientation = xlHidden

End Sub

End With