Custom configuration in web.config

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ASP.NET

I am trying to implement custom configuration in my web apps.
In my web config I have added the following sections:

<configsections>
    <section name="SecurityConfiguration" type="EncryptStringTesting.CustomConfiguration, EncryptStringTesting" /> 
  </configsections>  
  <securityconfiguration>
      <stringencryptdecryptpassword value="" />
 </securityconfiguration>

I've add a new class CustomConfiguration with following code:

Inherits System.Configuration.ConfigurationSection
#Region " Properties "
    <configurationproperty("value",> _
  Public Property value() As String
        Get
            Return CStr(Me("value"))
        End Get
        Set(ByVal value As String)
            Me("value") = value
        End Set
    End Property
    <configurationproperty("stringencryptdecryptpassword",>                          DefaultValue:="", _
                          IsRequired:=True, IsKey:=True)> _
   Public Property StringEncryptDecryptPassword() As String
        Get
            Return CStr(Me("StringEncryptDecryptPassword"))
        End Get
        Set(ByVal value As String)
            Me("StringEncryptDecryptPassword") = value
        End Set
    End Property

In my web page I am try to retrive my custom values:

Dim config As New CustomConfiguration
        config = System.Configuration.ConfigurationManager.GetSection("SecurityConfiguration")
    
        Response.Write(config.StringEncryptDecryptPassword.ToString)

When I call System.Configuration.ConfigurationManager.GetSection("SecurityConfiguration") getting nothing. Could you tell me why?