Cruise Control not functioning...

[asot]

After an extensive search for a similar problem in this forums and others, nothing found, so I am asking all of you guys for help...

My car: A X5 (E53) 3.0d (Feb. 2004) with 72,000Km
It's been a month since my problem - not be able to use (start) the cruise - speed- control...

Cruise control I/O was working (Green icon lights on board) but the (+) button is not working, so I can't set a cruising speed.
This problems appeared in my last two trips.

I visited an independent mechanic, who 's been servicing my car for the last year, he said it's an ECU problem (he says it's an expensive item to replace for such a small reason), diagnosed an "0189" speed control error with the diagnostic computer, REset it, but the problem isn't solved!!
Repeat the procedure (reset the "0189" error) and this time, even the I/O button is not working (no green light on board).

Keep in mind I ahve used the buttons for a lot of trips and a lot of hours and know very well their functions...

Any ideas? Had anybody out there had a similar problem and how was it solved?
I'm thinking any fuse? Some poor contacts inside the steering wheel?