Excel VBA Find and Replace Run Time Error 91

Sub Macro3()
'
' Macro3 Macro
'

'
    Sheets("Tally Data").Select
    Dim Rng As Range
    Dim C As Range
    Dim uSSo As String
    uSSo = "NA"
    Range("T11:T5010").Select
    With Selection
    Set C = .Find(What:=uSSo, After:=Range("T11"), LookIn:=xlFormulas, LookAt _
        :=xlPart, SearchOrder:=xlByRows, SearchDirection:=xlNext, MatchCase:= _
        False, SearchFormat:=False).Active
    If Not C Is Nothing Then
    ActiveCell.Replace What:="NA", Replacement:="", LookAt:=xlPart, _
        SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
        ReplaceFormat:=False
    Else
    Range("T11").Select
    Selection.End(xlDown).Select
    ActiveCell.Offset(0, 1).Select
    Range(Selection, Selection.End(xlUp)).Select
    Selection.FillDown
    Range("U11").Select
    Selection.End(xlDown).Select
    ActiveCell.Offset(0, 1).Select
    Range(Selection, Selection.End(xlUp)).Select
    Selection.FillDown
    End If
    End With
    Range("A1").Select
End Sub