There's been more than one report of electronic voting machines casting ballots in error. Observant voters caught the error, but there's not any way of knowing how many didn't.
What is a calibration error with an electronic voting machine? Somebody screwed up the computer code, whether intentionally, or by accident. I'd say both are responsible, but lean more to the intentional reason for most incidents. There is no "calibration". That's a word that is misused in this application.
Since voting machines are used by locals for entering candidate names, or ballot initiatives, the opportunity is there for fraud, and the data can easily be manipulated after an election.
The solution? No electronic voting. Paper ballots, voters get their finger dipped in indelible ink, and anyone caught intentionally trying to subvert votes is shot on sight. I have a feeling elections after this method is implemented would show a different view of the nation.