I got this code that is almost identical to your code except you have public object between the private classes, you are also missing the Import statement for System.Threading because Mutex manages threads.  Check the links below for VB code implementing Singleton Pattern. The first is your code and the second is the code from the first link. Hope this helps.

Namespace ProjectName.BLL

    Public NotInheritable Class WebIServer

        Private Shared Instance As WebIServer
        Private Shared _mu As New Mutex
        Public MyObject As New MyCom.Server

        Private Sub New()
            MyObject = New MyCom.Server
        End Sub

        Public Shared Function GetInstance() As WebIServer

            _mu.WaitOne()

            Try
                If Instance Is Nothing Then
                    Instance = New WebIServer
                End If

            Finally
                _mu.ReleaseMutex()
            End Try

            Return Instance

        End Function

    End Class

End Namespace

Imports System.Threading

Namespace Abstractvb.DesignPatterns

    Public Class Singleton

        Private Shared _singleton As Singleton

        Private Shared _mu As New Mutex()

        Private Sub New()

        End Sub

        Public Shared Function GetInstance() As Singleton

            _mu.WaitOne()

            Try
                If _singleton Is Nothing Then
                    _singleton = New Singleton()
                End If

            Finally
                _mu.ReleaseMutex()
            End Try

            Return _singleton

        End Function

    End Class

End Namespace

http://abstractvb.com/code.asp?A=1096

http://www.codeguru.com/columns/VB/article.php/c6563/