The delay affects people claiming education tax credits who filed returns between Feb. 14 and Feb. 22.
H&R Block, the tax preparing giant, says that some of its customers were affected but the company has resolved the problem. A limited number of other software companies have also had problems, but IRS spokeswoman Michelle Eldridge declined to name them.
About 6.6 million taxpayers are expected to claim the education tax credits. The IRS says about 10 percent of their returns are affected.
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