[a8 tech]

There will be a communication interuption between the dash(immobilizer is part of)and the engine control unit.The engine control unit has to be enabled from the dash to authorise start,even though the engine is cranking.This may require a fine eye cast over the electrical terminals and possible dash/ecu replacement.They need to recreate the fault and check that the dash has communication with the engine control unit for the start signal.Try looking inside the engine control unit e box housing.The housing is located under the bonnet next to the wiper motor.Water can enter the e box and corrosion of the connections can occur.The engine control unit sits above the water ingress so is rarely affected but beneath the ecu sits the main multiplugs for the engine bay and thet can become corroded.Just some thoughts to consider.