Microsoft Corp., the software giant worth an estimated $600 billion, said today that its free e-mail service had been partially crippled because it forgot to pay a $35 bill.

Some users of Microsoft's Hotmail service were unable to access their accounts over Christmas weekend, Kathy Gill, a Microsoft spokeswoman, confirmed.

The glitch was caused after Redmond, Wash.-based Microsoft failed to pay a $35 fee to Network Solutions Inc. for rights to the Internet domain name passport.com, which verifies user names and passwords for Hotmail and other services, Gill said. Herndon-based Network Solutions administers a domain name registry.

Hotmail has more than 52 million users around the world, but Microsoft said it was unclear how many had experienced problems.

The billing gaffe was discovered by Michael Chaney, an Antioch, Tenn., programmer who works with the Linux operating system, an upstart competitor to Microsoft's Windows platform. Chaney also covered the bill.

On his Web site at http://www.doublewide.net, Chaney said he paid the fee with his Mastercard on Christmas morning and on Tuesday received a call from a Microsoft executive thanking him.

Microsoft said it would refund Chaney the $35, although Chaney hinted his bailout was worth more.

"Microsoft is under no legal obligation to repay the $35 to me, and it doesn't really matter to me if they do or not. If they do . . . I would ask that when they make out a check they consider how much revenue would have otherwise been lost had this been down for another day or two, in addition to the inconvenience to people who rely on Hotmail as their only source of e-mail contact," Chaney wrote.