The problem isn't the close button. There are a pair of black boxes, an infrared transmitter and receiver, near the floor on the inside of your garage. If the beam between them is obstructed, the door will only close with constant pressure on the wall button as a safety feature.
Check to make sure the sensors are aligned first, then make sure nothing is obstructing them. The receiver is sensitive to sunlight, and the wiring connecting both boxes to the motor might be disconnected somewhere.
If these things check out, you probably just have defective sensors. If the machine is still under warranty, you should call tech support and explain the problem to them. They'll ship you a new pair. If the machine isn't under warranty, you can probably pick up a new pair of sensors at a local dealer and install them yourself.
Ben, July 2006