It seems trying to leave Cuba is a crime.
From an article in CUBANET:
SANTA CLARA, Cuba – July 28 (Guillermo FariÃ±as, CubanacÃ¡n Press / http://www.cubanet.org) – A group of dissidents from Villa Clara who tried to leave Cuba via GuantÃ¡namo Bay have been transported to a prison, although leaving the country without an exit visa is not a punishable crime.
Luis Enrique Junquera GarcÃa, Juan Carlos AlpÃzar Rodas, Aleixis Sotolongo DÃaz, Didier Arencibia PÃ©rez and Orlando RodrÃguez Salazar, all members of the Liberal Party of Cuba, tried to leave June 25.
Alexis LÃ¡zaro PÃ©rez Bernal, a relative of one of the men, said he had been advised that the group was being held at the Aguadores prison in Santiago de Cuba.