>The blackout's primary cause was a software bug in the alarm system at the control room of FirstEnergy, an Akron, Ohio–based company, which rendered operators unaware of the need to redistribute load after overloaded transmission lines drooped into foliage. What should have been a manageable local blackout cascaded into collapse of the entire Northeast region.
An engineer set the "state estimator" to manual mode at 12:40 pm, then at 1:30 pm went to lunch forgetting to put it back on auto. Half an hour later, a grounded wire set off the first outage and due to the system reporting bad information, a cascade occurred.
They had launched the new power model just a couple of months prior, but I don't think it was a software glitch. For a few more details, see https://news.ycombinator.com/item?id=12476001 and for the full report (238-page PDF) see https://www.energy.gov/sites/prod/files/oeprod/DocumentsandM...