Indufan is correct. You have been flaged for an additional security check at your point of departure. When you check in you boarding pass will have a code that states you must be reviewed. You may want to get to the airport a few minutes early.

I am Plt for 2 years running and get this about one every two months. No reason why but it never fails that if I can 't check in on line - I get the added security check.