The District voided 31,602 parking and traffic citations because of procedural blunders and other mistakes by its employees, costing D.C. more than $4.1 million in a year, the city’s inspector general has found.

“The District lost the opportunity to collect revenue of approximately $4.1 million,” Inspector General Charles Willoughby’s office wrote of the city’s performance in 2010. “We consider these dismissals to be preventable in most instances.”