Code UE is an unbalanced load error, usually shown when there is a very small load where the machine cannot redistribute the weight to balance it (because there isn't enough clothes to go around). I suppose it could also occur in a larger load where there are heavy items mixed with larger lighter items and the drum is full - here again, the machine wouldn't be able to balance the load due to the drum being full.
In some cases, a more serious problem exists requiring service, as in the case of either a loose sensor (easy to repair by a service tech) or a bad control board (easy to repair by a tech but you have to wait on parts).
Tom Chambers, November 2008