how can i fix my hi MY ULTIMA 1200 WM75?

hi MY ULTIMA 1200 WM75 washing machine, goes throught the washing cycle but when it comes to the spinning at the end it stops and the error message "check outlet pipes" comes up. I have had a plumber to look at it and he has checked the outlet pipes which are fine and checked a few of the sensors, but still no luck. He says the motor is fine, but that it maybe another sensor he is not aware of.\r\n
Any Idea what the problem is?