I have had the issue of the spoiler light flashing for months now, tried all the usual things, but was convinced that nothing specific was wrong, as in if I reset the car (by disconnecting the battery and reconnecting it) everything works for about 10 mins, IE the roof went up and down, spoiler went up and down, then the flashing light came back again and the roof wouldn't move, or the spoiler.

Took the car to Mercedes who charged £300 to tell me they couldn't find the fault!, tried a few of the suggestions here, still no fix.

Sent the ecu to a specialist, no fault found.

In desperation I took the ECU out, and the small unit next to the ECU (body control module I think?) and removed every plug, fuse etc, and cleaned all 50-60 pins.

I found one pin on the small white connector (first plug from the front on the bcm) had slight corrosion, and was tracing to an adjacent pin.

Cleaned it up, - put it all back - Light now off!. Roof and spoiler works fine! I have tried to re create the problem, engine on and off, roof up and down, spoiler up and down, open boot, close boot, etc etc,

So far all good news! Total cost to fix - zero! So, as they say, try the simple things first!

Hope this helps anyone else who gets the flashing light!