File opertation in VB.Net

imports system.io

Public Class Form1

    Public Sub MaintainintoFile(Optional ByVal StringtoWrite As String = "Error Not Trapped")

        Try

            Dim StartLog As Boolean

            Dim FName As String

            Dim LogDirName As String

            Dim BaseErr As String = ""

            Dim fs As FileStream

            Dim fileWrite As StreamWriter

            Dim dir As String

            StartLog = True

            dir = Application.StartupPath

            LogDirName = dir & "\Log\"

            If Not Directory.Exists(LogDirName) Then Directory.CreateDirectory(LogDirName)

            FName = LogDirName & "Log.log"

            If File.Exists(FName) Then

                fs = New FileStream(FName, FileMode.Append, FileAccess.Write, FileShare.Read)

                fileWrite = New StreamWriter(fs)

            Else

                fs = New FileStream(FName, FileMode.OpenOrCreate, FileAccess.Write, FileShare.Read)

                fileWrite = New StreamWriter(fs)

            End If

            fileWrite.Write(vbNewLine & CStr(Now) & ":" & StringtoWrite)

            fileWrite.Close()

            Exit Sub

        Catch ex As Exception

            MsgBox(Err.Description)

        End Try

    End Sub

End Class