XML : trying to understand with IRS MeF SDK

i have the sdk , and been running the demo app you get to build following the quick guide, but if someone here could answer me some questions, right now when the console app runs, after pressing option 3, log will have this Message : cert path validation failed: Unable to find valid certification path to requested end-entity cert and im a little lost there, their documentation is horrible btw if someone could shed some light here thanks