Ok, I too was in this situation and searched the entire internet with no luck. So, with luck I figured it out on my own. Here is what you do.
If your game "glitches" while trying to defeat the Baron, hit start and enter the sanctuary. Enter the Armory and go to the left side of the room containing Melee weapons. While facing the wall the top of the screen should say.
Melee Weapons
LT Set 1/2 RT
Of course LT and RT means Left and Right trigger, and Set 1 means you have more Melee weapons to choose from.
Hit the LT and scroll to the 2nd set of Melee weapons and select
THE SWORD OF THE BARON. Press start again to return to "The Game." Hit the cardboard Baron one time and it will fall to the ground, allowing you to save the princess. Then the achievment pops for 10 gamerscore and your quest continues. Tell me if this helps. And if your feeling in the giving mood, I am collecting Download Content. I bought the Legendary Edition at gamestop, So I have the Inquisitor Sword and Tattoo. If you ordered from Amazon, Or Walmart, Or Best Buy, and have an extra code to spare then Please email me one to
robbyinky@yahoo.com