Any time you drop bombs close to friendly troops, there's the possibility of mishap. Even smart bombs get stupid from time to time or they can be misaimed or given inaccurate targeting info. From an article by the BBC:

"In Washington, Pentagon spokeswoman Victoria Clarke said five US military personnel had been injured by a stray American bomb.

The satellite-guided bomb was dropped in an air strike to put down the prisoners' uprising, she said.

Three of the injured servicemen have been rushed to Uzbekistan for medical treatment. None of the injuries are life-threatening, she said."

There still are conflicting accounts about American fatalities. The DoD is saying no US servicemen are dead but it's possible a CIA agent died. A small number ("single digits" of British commandos have also been wounded but none are believed to have life threatening wounds.