What does the Ub error code mean and how do I resolve it?

The Ub code means spinning is not working due to an unbalanced load. Redistribute the laundry so it is spread out evenly in the tub, and make sure the washing machine is on a flat, stable surface. Note that washing a single large item such as a bathrobe or pair of jeans may result in an unsatisfactory spin and trigger the Ub code. (Page 50)