This comes from "jakenbake" on the RX 2nd gen forum which he discovered after encountering the "error 4" message that locked up his CD player with discs inside:

I unplugged the battery and that didn't work so I started to take the stereo out of the dash to take it apart. Before I unplugged the harnesses from the back, I noticed the label that tells you how to put the stereo in "shipping mode". With the car off, hold down "seek up" and "disc" at the same time. Continue to hold the buttons and turn the car to "ACC" mode. This immediately ejected the CDs and the word " SHIP" displayed on the screen. I pressed "LOAD" and that took it out of shipping mode and everything is working like normal.