I've ran part of the adventure that came with the Beginner Box and noticed it made no mention of why the ship was locked down. But all I did was quickly improvise and say the ship was locked down due to unpaid docking fees Trex owed from a previous visit and an issue that the female officer in command of the control center had against the Hutt and his lackeys. As for how the heroes learned about the ship being locked down, I simply told them that they had heard about it while in the cantina and again while they were at the junk shop.
Like most pre-made adventures, this one needs a little polishing by GMs. But overall, I think its a simple, fun game that was really designed to introduce FF's system and to get you right into the Star Wars universe, which I think they did an excellent job of doing.