I have same problem with 406 sri Turbo 1996. Happens about 6 times a year.
Puegeot dealer can't help as no fault recorded in ECU.
Found this web site and they have an article on mentioning this issue for
106 and advice on fixing. Follow link and search page for immobiliser.
formatting link
I'm going to ring them (ADS) in the morning to see if they can help me otherwise I'll have to scrap the car.Good luck.