Charging cable error

The other day I got in my car in the morning, and it had a message about some kind of charging problem. It only showed 9.5 miles of range, so it probably charged for about an hour the previous night before stopping. The charging cable had the power light on, and the error light flashing 3 times. Looking that up in the instructions, there is just an unhelpful note to contact Toyota dealer. It says "An electrical leakage is detected and charging is canceled, or there is a malfunction in the charging cable." I doubt the dealer knows anything. The cable works again after unplugging it. I can't think of any way there would be "electrical leakage". It wasn't on a GFCI outlet, but it was in a garage and everything was dry. Has anyone had this problem before?

 

In this case the brick was hanging from the receptacle, so maybe that was the problem. I've charged from that receptacle before without a problem, though. They really should have put a slightly longer cord on the wall side so it can rest on the ground.