// this code works fine.
public sealed class MyObject
{
    static ExtDeviceDriver devDrv;

    public MyObject()
    {
        devDrv = new ExtDeviceDriver();
    }

    public void Connect()
    {
        devDrv.connect();
    }
}

//this code causes exception.
public sealed class MyObject
{
    static ExtDeviceDriver devDrv;

    public MyObject()
    {
        // do not create devDrv here.
        //devDrv = new ExtDeviceDriver();
    }

    public void Connect()
    {
        if (devDrv == null)
            devDrv = new ExtDeviceDriver();
        devDrv.connect();
    }
}

public class MyObject
 {
   static ExtDeviceDriver devDrv;

  static MyObject()
  {
    devDrv = new ExtDeviceDriver();
  }

  public void Connect()
  {
    devDrv.connect();
  }
 }