I completed the game a while ago (both story and poppet academy) and decided to try to get the trophies. Once I got the "Senior Creator" trophy I moved onto getting the story trophies. But all the levels are now locked for some reason. When I go on the world map and hover over "Prologue" it says 98% prizes won, but it also says 0 out of 5 levels completed? And when I open it up and try to go on the levels, all of them are locked other than the introduction. I was playing the story last night and it was fine; why have I suddenly been locked out of all of the levels? And how do I unlock them again? I don't think it's deleted my game progress because it still says how many of the items I have found. Any help would be appreciated!

Yeah, this is a cute little bug that's been floating around for a bit now. What i've read (and what sometimes has worked for me) is to just leave your cursor over play for a bit, but not actually go into the adventure. After about a half-minute or so, it should display as normal and unlocked again. If you actually go into the Adventure, the levels are stuck as locked until you go through them all again.
This is the reason why i finally broke down and used timesaver levels to pick up all the prize bubbles. i'd gotten all the trophies i was likely to get on my Jside account. When those servers got shut down, i replayed through on the US-side account (to at least open up the multi-player necessary levels). But my progress kept getting reset. Now i just leave story mode as is.

Unfortunately hovering over the adventure map didn't work for me I've replayed the entire game, which, after initially feeling p angry, I really enjoyed and remember why I loved the game so much. Only trouble now is acing all the levels!

Glad you at least got some joy out of it! i just don't have the time for another full play-through, myself.
Good luck with getting the Aces! Some of those levels can be pretty tough.

Haha, I have that bug too!

I really want to enjoy LBP3's story mode, but it's difficult. I leave the story mode alone too and I used timesaver levels (Which was the last thing I wanted to do in a LBP game).

In the end I have 100% of the items and I am not playing story mode at all.