"g) As a result of its failure, the active inertial reference system transmitted essentially diagnostic information to the launcher's main computer, where it was interpreted as flight data and used for flight control calculations."
So the handler in the processes existed but it effectively confused the main computer. The units shut off but before that sent "the diagnostic." For which there was no handler at all in the main computer. And even more interesting, these processes weren't even needed for the flight. The main computer were able to just ignore such input and the flight would have continued (R1).
http://www.math.umn.edu/~arnold/disasters/ariane5rep.html
"g) As a result of its failure, the active inertial reference system transmitted essentially diagnostic information to the launcher's main computer, where it was interpreted as flight data and used for flight control calculations."
So the handler in the processes existed but it effectively confused the main computer. The units shut off but before that sent "the diagnostic." For which there was no handler at all in the main computer. And even more interesting, these processes weren't even needed for the flight. The main computer were able to just ignore such input and the flight would have continued (R1).
Brittle.