My son is playing this on our PS3 and ran into a similar problem. He spent about two days patiently working on the star destroyer, then finally beat it. Then he beat the next level and was wandering around in the death star.
Guess what happens when we load the game last night? Back at the star destroyer. There was no freeze, it just lost all that progress and the saved games are nowhere to be found. He's about to put it down rather than go through the star destroyer level again, and I don't blame him.
I haven't even started the game myself. If this is how it's going to be, I'm not sure I want to!
I'm going to look around this week and see if I can find a saved game to download and get him back where he was before the hiccup. *sigh*