Hmmm.... maybe this then

Sub test()     
    Dim ws As Worksheet
    Dim Namebase As String
    Dim SheetExists As Boolean
    Namebase = Format(Date, "dd,mm,yyy")
    SheetExists = False
    With ThisWorkbook
        'Check if the Sheet exists
        For Each ws In .Worksheets
            If ws.Name = Namebase Then
                SheetExists = True
                Exit For
            End If  
        Next
        If SheetExists = False Then
            'If the sheet doesn't exist,  then create
            .Sheets.Add(After:=.Sheets(.Sheets.Count)).Name = Namebase
        End If
    End With
End Sub