H&R Block has been bombarded with complaints in recent days over errors on an Internal Revenue Service tax form that will cause thousands of refunds to be delayed four to six weeks.

The error on Form 8863 for education tax credits affects more than 600,000 refunds to H&R Block clients, according to the IRS, although the nation’s largest tax preparer has not said publicly how many clients are affected, nor has it said the number affected in metro Atlanta.

The delay in finalizing tax returns and getting them back to clients also could hinder efforts to file U.S. Department of Education applications for federal student grants and loans, since the applications rely on information from the returns.

Clients have flooded H&R Block’s Facebook account with complaints, posting hundreds of comments over the past few days.

“I had my taxes done so that my refund would come in time for spring break — so I could do something fun with my kids for once during the year,” posted Jessica Peterson Daniels. “Unbelievable!”

In a statement Tuesday to The Atlanta Journal-Constitution, company spokesman Gene King said, “Any problems that occurred with Form 8863 have been fixed.”

“The IRS has informed us and other impacted providers that they are currently processing returns and should be able to more accurately provide refund timelines via its “Where’s My Refund?” website,” King said.

Without providing more details, H&R Block blamed “an issue with a limited number of software company products” used for filings between Feb. 14 and Feb. 22.

U.S. taxpayers had already faced delays in their refunds after the start of this year’s tax filing season was pushed back. IRS forms had to be revised to reflect changes related to “fiscal cliff” legislation earlier this year.

IRS spokeswoman Michelle Eldridge told Marketwatch.com that H&R Block essentially left mandatory fields on Form 8863 blank when they called for responses of “No.”

The IRS contacted many taxpayers about the error and had them resubmit their returns.

Form 8863 is used to claim tax credits for qualified expenses paid to postsecondary education institutions. Credits can be claimed if a taxpayer, spouse, or a dependent was a student beginning in 2012 or the first three months of 2013. There are two education credits: the American opportunity credit and the lifetime learning credit.

Information on tax returns is also used for the Free Application for Federal Student Aid, which is the basic qualifying form used for all federal student aid programs, and many state, regional and private student aid programs.

Some clients have complained that their chances of getting financial aid are jeopardized because the FAFSA applications can’t be completed. The IRS says applicants can manually enter their financial data on the FAFSA website and update it when they get their returns.

“I’m charging H&R Block 10 percent interest for every day over 21 days that my refund is late,” Vincent Santa Maria posted on Facebook.