National Grid USA president Tom King said Tuesday that the company has made "significant improvements" to a glitch-ridden computer system that resulted in thousands of employees being shortchanged on their pay in the weeks after superstorm Sandy.

On a conference call to announce National Grid's $40 million investment in transmission-line developer Clean Line Energy Partners, King was asked by Newsday if the company had fixed bugs in the computer system, which reduced employee paychecks to anywhere from zero to 40 hours despite considerable storm-related overtime.

The glitches have prompted a class-action lawsuit by employees, and complaints by unions to the state attorney general's office and the U.S. Department of Labor.

King said changes have been made in the system through each of three payrolls since Sandy, and that each has shown "significant improvements."

However, "We assume it will take us a few more payrolls to get it all ironed out," King said.

King said the problem stemmed from the company's migration, as Sandy struck, to a new financial computer system from two previous systems after more than a year of preparation. "As with any new system, you always run into unavoidable hang-ups," he said.

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One employee said Monday that he'd recently been paid for eight hours of work despite a backlog of more than 300 hours of pay. He and others said the mistake resulted in disrupted travel plans over the Thanksgiving weekend, canceled vacations and in some cases employees remaining home from work for lack of cash to cover gas and other expenses.

King said National Grid will fix the problem and make certain employees are paid properly.

"Everyone will be fully compensated for all their work," he said.