DIAGNOSIS The infrared signals from the Home Base aren't being seen by the robot, usually due to placement or dirty sensors.
FIX Ensure the dock is in an open area with at least 3 feet of clear space on both sides and 4 feet in front. Move any objects, especially dark furniture or baskets, away from the front of the dock. Wipe the two circular IR receiver windows on the front bumper of the robot.
IF THAT DIDN'T WORK Check that the two IR lenses on the top of the Home Base are clean and unobstructed. Also, direct sunlight or very bright light shining on the dock can drown out its IR signal. Try a slightly shaded location.
HEADS UP The robot needs to 'trip' over the dock's forward signals to align. Start a 'dock' command from the same room as the dock, not from across the house.