TheTrainLine, which manages rail retailing for Virgin Trains, was meant to send the email to only a small group of customers but sent it to tens of thousands of Virgin Trains customers by mistake.
Virgin Trains sent a second email apologising for the error and offered customers the chance to win tickets to the event instead.
The email read: "We realise that we might have got you all excited about the prospect of a day at The Grove, and would like to offer you the chance to win one of three places at this event."
Virgin Trains said it was a genuine mistake and felt it acted quickly to apologise.