Two guys may not have passed the physical:

Green Bay - The Packers announced the signing of 19 undrafted rookies, two fewer than the Journal Sentinel had reported as agreeing to terms this past week.

Two of the players - Georgia Tech safety Demond Smith and Alcorn State cornerback Warren Gatewood -- were not on the list and not at practice Friday morning.

Typically, it means that there was an injury concern the Packers had and so they voided the agreement.
http://www.jsonline.com/blogs/sports/378463401.html