Help!Sourdough Bread stuck to the dutch oven!?!

I have been baking “no knead sourdough bread” for a while now. ALWAYS with fabulous results in a preheated dutch oven. Today a major flop. The bread got seriously stuck on the dutch oven I use (and have used every since I started baking) What did I do wrong?!? Also does anybody have some input in baking with a Romertopf? Pros and Cons. Thank you.

Parchment paper on the bottom of the baking vessel? When I was just starting out someone had to tell me that. I had just been using a Pyrex vessel with nothing on the bottom. Sometimes the loaf fell right out and sometimes it stuck and had to be pried out.