Generate Unique Random Numbers in ASP.NET

Public Function RandomNumbers(Upper As Integer,   Optional Lower As Integer = 1, Optional HowMany As Integer = 1, Optional Unique As Boolean = True) As Variant
    On Error GoTo LocalError
    If HowMany > ((Upper + 1) - (Lower - 1)) Then Exit Function
    Dim x           As Integer
    Dim n           As Integer
    Dim arrNums()   As Variant
    Dim colNumbers  As New Collection
   
    ReDim arrNums(HowMany - 1)
    With colNumbers
        'First populate the collection
        For x = Lower To Upper
            .Add x
        Next x
        For x = 0 To HowMany - 1
            n = RandomNumber(0, colNumbers.Count + 1)
            arrNums(x) = colNumbers(n)
            If Unique Then
                colNumbers.Remove n
            End If
        Next x
    End With
    Set colNumbers = Nothing
    RandomNumbers = arrNums
Exit Function
LocalError:
    RandomNumbers = ""
End Function


Public Function RandomNumber(Upper As Integer, Lower As Integer) As Integer
    Randomize
    RandomNumber = Int((Upper - Lower + 1) * Rnd + Lower)
End Function