custom membership provider

I am working on custom membership provider model in asp.net 3.5.
I have created Custom database a class and made changes in web.config file.
On running  I getting Error:ConnectionString Property is not initialized.
Can anyone help in the code what is wrong???
here is the full code:
Web.config file:
<connectionStrings><add name="CustomDatabaseConnectionString" connectionString="Data Source=.\S ...