Make sure the blanket is not intersecting with the figures or the bed at any point. If the simulation hangs that way, it's often because it's intersecting with a collision object somewhere.

What are you using for the blanket? The high-res square?

It might help to save your work, exit Poser, and get back in. When the Cloth Room isn't working right, it's often because there's not enough memory. Closing Poser and getting back in frees up memory and usually fixes the problem.

It should work. I've done it.