I hesitate to suggest this is the answer in your case, but I have had this problem with my 407SW. I discovered I was catching the central button on the remote when unlocking the car. this wasn't noticable until I started the engine, then I got the warning. Sorry I can't offer any other solution.
My 407SW started to have the same symptoms about 4 weeks ago. About the same time I noticed the soft button under the the rear wiper stopped working. In normal day to day use I never use the feature of opening the glass, I simply open the complete tailgate. However I do open the glass when cleaning the vehicle, this is how I noticed the soft button stopped working. Anyway I put two and two together, and assumed the two problems were linked. I opened the glass, ( with the remote ) prised off the plastic cover, covering the rear wiper workings on the inside surface of the glass. I then simply disconnected the wireing to the soft switch. Everything has been fine since then. The glass still opens as normal with the remote for cleaning, but it has never popped open accidently since. If you dont use the soft button, I suggest you do as I did.