Russian sources [1][2] don't tell us much more besides that the error is probably in software, the people responsible are preparing for the worst-case scenario and that the damage to the budget is in ballpark of $160MM (of which ~$40MM are insured).

[1] http://www.kommersant.ru/doc/1812141

[2] http://www.vedomosti.ru/newsline/news/1415670/situaciya_s_fo...