What is the maximum weight limit for using Lower Anchor Connectors with the internal harnesses?

Do not use the Lower Anchors of the LATCH system to attach this child restraint when restraining a child weighing more than 20.4 kg (45 lbs) with the internal harnesses. Instead, install this child restraint with the vehicle seat belt (not Lower Anchor Connectors) when the child weighs more than 20.4 kg (45 lbs). (Page 9)