I had this error on my MBr and wanted to post this possible solution in the event someone else gets this error.
The gate is pulled open by a spring attached to the solenoid under the playfield (pic 1). When I checked under the pf I found that the spring was disconnected (pic 2). With a pair of needle-nose pliers I was able to pull the spring and reconnect it.
I powered the game back up and ran a few balls through the loop which cleared the error.
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