You inadvertently performed the reset sequence.
For those that are interested, most of the AEG Lavamat washing machines require the following to reset:-
1) Hold in the Pre-wash & soaking buttons TOGETHER;
2) At the same time, turn the knob clockwise from the OFF position, to "Short Spin". All the LEDS light up.
3) turn the knob anti-clockwise to "energy saving"
4) Machine is reset and the door release clicks.
Switch your machine off and then back on again. Hey presto. I know it works as I did this last night on my AEG 72620 Update. It cleared the C9 code although it returned as I hadn't fixed the root cause of failure...
Phil
July 2008