Problem in Connection String in VB.NET

Question

Hi all,

Below is the connection string in my app.config file in Window forms application.
<connectionStrings>
<add name="ConnectionString1" connectionString="Data Source=.;uid=sa;pwd=wintellect;database=test;" providerName="System.Data.sqlclient"/>
</connectionStrings>
 I got this error : "Object reference not set to an instance of an object." in vb.net windows application for sql connection string here is the code:
Dim str As String= ConfigurationManager.ConnectionStrings("ConnectionString1").ConnectionString