Tuesday's 3-2 loss to Scunthorpe left North End second bottom of the table and staring at the dismal prospect of a relegation dogfight.
They have conceded 26 league goals in 12 games and Ferguson said: "The players said themselves that you can't legislate for individual errors.
"That's not having a go at anyone it is just factual and it is what has happened on Tuesday night and other times this season. If they don't happen we win the game."
Source: PA