SAN JOSE, Calif. – Thousands of TurboTax Online customers experienced a weekend of frustration after an “outage” blocked them from filing their taxes in the first days after tax agencies started accepting returns.

Intuit of Mountain View, Calif. – which dominates the tax software market with its TurboTax software – said the problem stretched from about 1 p.m. Saturday to 10 p.m. Sunday.

One customer complained the system was still plagued with problems Monday afternoon, and the TurboTax Web site was peppered with complaints about continuing error messages on Monday. But TurboTax spokeswoman Julie Miller said some of those errors reflect instances in which the Internal Revenue Service rejected improperly completed e-filed returns.

The weekend outage was “caused by human error during a routine hard drive update,” Miller said. It was not related to the meltdown last April that caused about 200,000 customers to miss the tax-filing deadline and spurred Intuit to offer $15 million in refunds.

Miller estimated the weekend problem affected customers in the “low single-digit thousands” when they tried to prepare, amend or check their tax returns using the online software available at www.turbotax.com. It did not affect customers who bought the desktop TurboTax product, nor Intuit’s software for professional preparers, she said.

“We understand that caused a lot of frustration,” Miller said. “We deeply regret any inconvenience that it caused to our customers.”