When the rollers are compressed a small amount of sawdust builds up under the ends and won't allow the roller to decompress. When measuring the board the board sensor doesn't look for the edge until the roller decompresses. If it doesn't decompress the board will continue until it looses contact with the brass tracking roller and gives you the message. To fix it, crank the head up to near the top and reach inside and squeeze the roller so it is in a compressed state. If you have difficulty holding the roller up you can use a board placed on edge and crank the head down on it to lift the roller. Use compressed air to blow out both ends of both rollers. On the left side there is a rubber washer. Blow out the sawdust on both sides. This is a common problem and this procedure usually fixes it. If it doesn't, you may have to remove the keypad end to blow out more of the sawdust. If that still doesn't work, you have other problems. Check the board sensor for sawdust inside the plastic lens.