I want to store the username/password information of my windows service 'logon as' user in the app.config.

So in my Installer, I am trying to grab the username/password from app.config and set the property but I am getting an error when trying to install the service.

It works fine if I hard code the username/password, and fails when I try and access the app.config

```
public class Blah : Installer
{

    public Blah()
    {

        ServiceProcessInstaller oServiceProcessInstaller = new ServiceProcessInstaller();
                ServiceInstaller oServiceInstaller = new ServiceInstaller();            

                oServiceProcessInstaller.Account = ServiceAccount.User;

        oServiceProcessInstaller.Username =             ConfigurationManager.AppSettings["ServiceProcessUsername"].ToString();

    }
}

```