What about a higher than normal solar activity and auroras?
But there's something quite simple that could be done: printing each ballot and depositing it in a sealed box -- just like a regular voting system. After announcing the votes as counted by the machines, the process of counting the ballots can begin and the election results would only be promulgated if both counts match.
The votes are actually printed in paper, just in case the voting data is damaged
"Just think of a computer as hardware you can program." -- Nigel de la Tierre