A typo has cost the Japanese Mizuho Corporation some 27 billion yen. Losses may rise to 100 billion yen. Essentially, they wanted to sell one share for 610000 yen, but instead sold 610000 shares for 1 yen.
27 billion yen is around 128 million pound sterling at today's rates.
What makes the story particularly amusing is that they sold 42 times more shares than are actually in existence and "since the number of sold shares exceeded the number of existing shares, there is a possibility that Mizuho may not be able to hand shares over to the investors who bought them."
Boringly, it isn't quite that much of a discount as the Japanese market has rules which limit price fluctuations.