Hi oxido! I can feel your pain. Last year I had a same problem as you, and few days back it came back. Last time it was because gas door actuator was not working->fixed by unplugging the electric connector from the gas door actuator.
Now, when the problem accured again, I first chekked rear...
I had same problem. In my case the problem was that the gas tanks door wouldn't lock. I took off the electric connector from gas door actuator and I made shortcut with those two cables. It's been working since then.