SSIS Script Task to change encoding

I am want to take a CSV output (which is UTF-16) and converting it using a script task. The reason is that I need to send the file to 3 different customers/suppliers that have different encoding.

I have the following .NET code but it keep throwing amd error.

Error: Failed to lock variable "C:\EXPORT.csv" for read/write access with error 0xC0010001 "The variable cannot be found. This occurs when an attempt is made to retrieve a variable from the Variables collection on a container during execution of the package, and the variable is not there. The variable name may have changed or the variable is not being created.".

Imports System
Imports System.Data
Imports System.Math
Imports System.Text
Imports System.IO
Imports Microsoft.SqlServer.Dts.Runtime

Public Class ScriptMain

    ' The execution engine calls this method when the task executes.
    ' To access the object model, use the Dts object. Connections, variables, events,
    ' and logging features are available as static members of the Dts class.
    ' Before returning from this method, set the value of Dts.TaskResult to indicate success or failure.
    ' 
    ' To open Code and Text Editor Help, press F1.
    ' To open Object Browser, press Ctrl+Alt+J.

    Public Sub Main()
    	'
    	' Add your code here
        '
        Dim inputFileName As String = Convert.ToString(Dts.Variables("InputFileName"))
        Dim outputFileName As String = Convert.ToString(Dts.Variables("OutputFileName"))

        If Not File.Exists(inputFileName) Then
            Throw New Exception("The input file could not be found.")
        End If

        ConvertFile(inputFileName, Encoding.Unicode, outputFileName, Encoding.UTF8)

        Dts.TaskResult = Dts.Results.Success
    End Sub

    Private Sub ConvertFile(ByVal inputFileName As String, ByVal inputEncoding As Encoding, ByVal outputFileName As String, ByVal outputEncoding As Encoding)
        Using reader As New StreamReader(inputFileName, inputEncoding)
            Using writer As New StreamWriter(outputFileName, False, outputEncoding)
                Dim line As String
                While (line = reader.ReadLine()) <> Nothing
                    writer.WriteLine(line)
                End While
                writer.Flush()
                writer.Close()
            End Using
        End Using
    End Sub
End Class