More than 500 DeKalb school district employees weren’t paid on time Friday thanks to data entry errors and a transition to a new payroll system, district officials said this week.

Superintendent Devon Horton sent a memo to all employees Monday apologizing for the delays. “We recognize the distress this situation caused and promise to learn from it to prevent any recurrence in the future,” read the memo, obtained by The Atlanta Journal-Constitution.

More than 500 employees were affected, and 65% of the issues were data entry errors and 35% were linked to the new payroll system, district spokesman Donald Porter said. Horton’s memo had similar information. District officials did not further explain the issues.

The majority of the affected employees were new to the district or had transitioned to new roles this year, officials said. DeKalb is the state’s third-largest school system and has more than 14,000 employees.

The payroll delays were first reported by FOX 5 Atlanta on Friday. The district initially reported that 300 employees were impacted, and later amended that to more than 500. Most of the problems were resolved by Friday night, Porter said in an emailed statement. As of Tuesday afternoon, 29 “unresolved payroll discrepancies” remained.

The school system spent more than $20 million to transition to a new software system to manage its human resources and financial processes. The new system from Tyler Technologies took over payroll this summer, district staff reported. The district originally contracted with the company in 2016 — and auditors have cited the lengthy implementation as a vulnerability that could leave room for accounting errors and financial waste.

Horton directed relevant staff to take additional, comprehensive measures by Sept. 15 to ensure a smooth and precise payroll process, Porter said.