A software upgrade is to blame for security cameras going dark at the McClellan-Palomar Airport in Carlsbad Monday before an unattended backpack prompted evacuations at the terminal and restaurant.

Returning from a trip to Europe, Kim Rosner accidentally left her green REI backpack behind when her son picked her up from the airport.

By the time she returned for it Monday evening, Carlsbad Police had cleared the area and called in the San Diego County Sheriff’s bomb squad to detonate the suspicious bag.

Rosner rushed up just in time to claim it.

"Accident, totally. Felt awful, but thankfully it was nothing to be concerned about," she said.

Rosner told NBC 7 that officials said their surveillance cameras were down, so they could not see who left the bag.

Airport Manager Olivier Brackett explained that when security spots an unattended bag, it is their procedure to look at surveillance video to see if a passenger flying in accidentally left it behind.

"So if I can determine that person was screened before they arrived at the airport, then that bag is pretty safe, and at that point we'll clear the bag,” said Brackett.

But a programming issue stopped video from recording onto the server. The system had just undergone maintenance on Saturday.

Brackett said the cameras themselves were working properly, but they did not realize the system had a problem until they tried to playback the video Monday.

Had the system been recording, Brackett said, they would most likely have seen Rosner posed no threat.

“When we noticed that the video wasn’t being recorded, we reverted to our existing backup protocols and called Carlsbad PD,” he said. Police in turn called the sheriff’s bomb squad, which ordered an evacuation of the area.

One camera in the area was recording correctly but at a difficult angle, Brackett said. The bag was tucked behind a trash can, next to a bench, so investigators were not able to confirm it was the bag in question.

The surveillance system is running properly now.

According Brackett, incidents like this are very rare. Airport security has an issue that requires them to check the security camera footage less than once a year, he said.

The airport, situated off Palomar Airport Road east of Interstate 5, houses about 283 aircraft, according to its website. In 2013, Palomar handled 160,290 takeoffs and landings.