JORDAN ROBERTSONSAN FRANCISCO (AP) â¿¿ A clerical error landed Kathleen Casey on the streets. Out of work two years, her unemployment benefits exhausted, in danger of losing her apartment, Casey applied for a job in the pharmacy of a Boston drugstore. She was offered $11 an hour. All she had to do was pass a background check. It turned up a 14-count criminal indictment. Kathleen Casey had been charged with larceny in a scam against an elderly man and woman that involved forged checks and fake credit cards. There was one technicality: The company that ran the background check, First Advantage, had the wrong woman. The rap sheet belonged to Kathleen A. Casey, who lived in another town nearby and was 18 years younger. Kathleen Ann Casey, would-be pharmacy technician, was clean. "It knocked my legs out from under me," she says. The business of background checks is booming. Employers spend at least $2 billion a year to look into the pasts of their prospective employees. They want to make sure they're not hiring a thief, or worse. But it is a system weakened by the conversion to digital files and compromised by the welter of private companies that profit by amassing public records and selling them to employers. These flaws have devastating consequences. It is a system in which the most sensitive information from people's pasts is bought and sold as a commodity. A system in which computers scrape the public files of court systems around the country to retrieve personal data. But a system in which what they retrieve isn't checked for errors that would be obvious to human eyes. A system that can damage reputations and, in a time of precious few job opportunities, rob honest workers of a chance at a new start. And a system that can leave the Kathleen Caseys of the world â¿¿ the innocent ones â¿¿ living in a car.