UPDATE 01/04/2015 5.20pm Bloodborne's game-breaking bug has been fixed in its latest patch.
The 1.02 update now ensures that the necessary Lunarium Key appears where it should.
While not stated in the patch notes, it's been widely reported that this also fixes the item duplicating exploit that allowed someone to breeze through the game in 40 minutes.
ORIGINAL STORY 27/03/2015 7.24pm It looks like Bloodborne has a game-breaking glitch that can completely halt player progress about a third of the way through the adventure. Thankfully, From Software and Sony are aware of this and an update is in the works to fix it.
As reported by Destructoid, the glitch involves a mandatory item called the Lunarium Key not appearing following a boss fight. Apparently this game-breaking bug only occurs when one enters another player's game in the Forbidden Woods area. Apparently it doesn't affect everyone, but just to be safe you should probably keep to solo play in the Forbidden Woods until you've obtained the Lunarium Key.
Sony said update 1.02 will alleviate this problem, and we can expect that next week. This update will not shorten load times, however, though that's still being worked on for a later date.