LG TROMM washing machine says door is open but it is closed
According to this parts page: http://www.searspartsdirect.com/model-number/wm2688hwm/3204/0153200.html

you probably need a new washer door lock switch: http://www.searspartsdirect.com/lg-washer-parts/6601ER1004C/0026/795/model-WM2688HWM/3204/0153200.html

Part number 6601ER1004C; it's available from Amazon, both quickly (and more expensive) and cheaper (and more slowly).

To confirm, see if you can figure out how the door latches closed, and where the switch is, and then try operating it by hand.