Well the configuration file only needs to be read once and the best time to do that, I would suggest, is in the Load eventhandler of the startup form.
The ReadConfig() method should then place the configuration variables in private static fields of the startup form class and expose them to the other classes using public readonly static properties.
Judging by your <a target="_new" href="http://www.csharpfriends.com/Forums/ShowPost.aspx?PostID=54272">other thread</a>, Login is your startup form and so you already have ReadConfig() in the right form and are calling it from the right place (Login_Load). So all you need now is some static fields/properties to store/expose the settings. For example:
public partial class Login : Form
{
private static string someSetting; // null by default
public static string SomeSetting
{
get { return someSetting;}
}
private void Login_Load(object sender, EventArgs e)
{
ReadConfig();
}
private bool ReadConfig()
{
if (IsConfigAvailable())
{
someSetting = someString; // read from config file
return true;
}
else
{
// etc
return false;
}
}
// other code
}
The setting can now be read from another form with a line like:
string someSetting = Login.SomeSetting;
As it's static, there's no need to bother getting a reference to the Login form instance.
If there are a lot of settings, you could create a separate class to store them all and then have just the one static property which returns an object of that class.