Script Task Error?

I have the following code inside a Script task:

Imports System

Imports System.Data

Imports System.Math

Imports Microsoft.SqlServer.Dts.Runtime

Imports System.Collections

Public Class ScriptMain

Public Sub Main()

Dim nm As String = "ship_metrics_rpt_*.csv"

Dim files As ObjectModel.ReadOnlyCollection(Of String) = My.Computer.FileSystem. _

GetFiles(CStr(Dts.Variables("MainPath").Value))

If files.Count > 0 Then

Dim dic As Generic.SortedDictionary(Of Date, String)

For a As Integer = 1 To files.Count

If files(a) Like nm Then

Dim nfo As System.IO.FileInfo = My.Computer.FileSystem.GetFileInfo(files(a))

dic.Add(nfo.CreationTime, files(a))

End If

Next

If dic.Count > 0 Then

Dim FinalFiles(dic.Count - 1) As String

Dim count As Integer

For Each kvp As Generic.KeyValuePair(Of Date, String) In dic

FinalFiles(count) = kvp.Value

Next

End If

End If

Dts.TaskResult = Dts.Results.Success

End Sub

The following exception gets thrown at "If files.Count > 0 Then"

"Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index"



Why?



Thanks for your help