Webber lost all telemetry data and KERS on the formation lap, which contributed to a poor getaway and wrecked his efforts in his home grand prix.
Red Bull initially suspected Webber's problem was caused by a failure of the standard ECU, which is supplied by McLaren Electronic Systems (MES).
However, post-race inspection by MES has pointed to an issue in the garage instead.
Peter van Manen, the managing director of MES, told AUTOSPORT: "There was an issue with Mark Webber's data system in the garage during the formation lap. The ECU on the car was fine.
"We regret any disruption caused to Mark's preparations for the start of the race and will continue to work with the team to prevent any recurrence."
McLaren introduced a new specification of ECU this year as part of the transition to the new 2014 turbo engine rules.
There had been some teething issues with the new units during pre-season testing, but progress has been made and McLaren team principal Martin Whitmarsh said his company would keep striving to improve them.
"It has been a slog, and it is not perfect," he said. "I don't want to be defensive about our electronics but if you undertake to supply these things, then people expect them to be faultless.
"It was a completely new ECU, with completely new software, and I think probably all of us have become blase because these systems had been so bullet proof."