Sort Macro Run-time error '1004': Application/Object-defined error.

Hi,

I am trying to create a piece of VBA code which sorts some data. However on the one sheet there are multiple sets of data to be sorted in alphabetical order. Data may also be added and removed so I am trying to use variables to set the sort range. Here is the code which I am using:

Range("A3").Select
  
    cellOne = ActiveCell.Address
    
    ActiveCell.Offset(0, 21).Select
    Selection.End(xlDown).Select
    ActiveCell.Offset(-3, 0).Select
    
    cellTwo = ActiveCell.Address
    
    Range(cellOne, cellTwo).Select
    ActiveSheet.Sort.SortFields.Clear
    ActiveSheet.Sort.SortFields.Add Key:=ActiveSheet.Range(cellOne & ":" & cellTwo), SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:= _
        xlSortNormal
    With ActiveSheet.Sort
        .SetRange Range(cellOne & ":" & cellTwo)
        .Header = xlNo
        .MatchCase = False
        .Orientation = xlTopToBottom
        .SortMethod = xlPinYin
        .Apply
    End With

The error "Run-time error '1004': Application-defined or object-defined error." appears on the .Apply line.

If anyone could point me in the right direction it would be appreciated.