Connection string issue??

Hi
 
I am trying to use a login control using wisual web developer 2008 with a SQL Express database. evrything is on my local machine at the moment.
This is the script I am using:
protected void Login1_Authenticate(object sender, AuthenticateEventArgs e)
{
 Boolean blnresult;
 blnresult = false;
 // Pass UserName  and Password from login1 control to an authentication function which will check will check the user name and password from sql server.
 // Then will retrun a true or false value into blnresult variable
 blnresult = Authentication(Login1.UserName, Login1.Password);
 // If blnresult has a true value then authenticate user
 if (blnresult == true)
 {
      // This is the actual statement which will authenticate the user
      e. ...