The government has pointed the finger at the Transener energy management firm, saying improper reprogramming of the electricity system was responsible for last month's dramatic power outage.
The error, which came following the installation of a bypass on a major transmission line, caused the black-out, officials said. Tens of millions of people in Argentina and Uruguay= without power for more than half a day.
Energy Secretary Gustavo Lopetegui told a congressional committee on Wednesday that the Transener company that operates the lines failed to account for and reprogramme an emergency system after replacing a high-voltage tower. So when a short circuit hit the grid, the suddenly imbalanced system didn't adjust to it as planned and the grid collapsed.
"The Argentine electrical system is robust, [but] a chain of failures led to collapse," Lopetegui said as he faced questioning over the unprecedented shutdown.
He described the cause as "an operational error by the company Transener."
Transener, which controls some 18,000 kilometres of power lines throughout the country, issued a statement of apology late Wednesday.
Lopetegui said regulators will determine what penalties to apply, explaing that the conclusions drawn were only preliminary, with a full report expected in "45 days to a month."
According to regulations, penalties can run as high as 10 percent of Transener's annual earnings or 50 percent of its monthly income. According to the firm's listing on the Buenos Aires Stock Exchange, that means a fine would not go higher than an estimated US$9 million. The company is co-owned by the private energy firm Pampa Energía and state company IEASA.
"This operational error has been recognised by Transener in its reports," he added.
An estimated 44 million people in Argentina and 3.4 million in Uruguay were left without power for 14 hours on June 16 in the now-infamous shutdown. Isolated power cuts also hit parts of Paraguay and southern Brazil.