(Updates throughout with further details and comment from Research Corporation Technologies lawyer and Microsoft spokesman.)

By Brent Kendall

Of DOW JONES NEWSWIRES

WASHINGTON -(Dow Jones)- Reviving a $500 million patent lawsuit against Microsoft Corp. (MSFT), a federal appeals court ruled Friday that a trial judge was too quick to throw out claims alleging that the software giant infringed six patents related to digital imaging.

The patents, which claim certain printing and computer display technologies, are owned by Research Corporation Technologies Inc., a not-for-profit technology company based in Tucson, Ariz.

The company sued Microsoft in 2001, arguing that the printer commands in Microsoft Windows and other Microsoft products infringed the patents.

An attorney for RCT said Friday that the company is seeking "in excess" of $ 500 million in damages.

A federal trial judge in Arizona had thrown out RCT's patent claims, saying the company improperly hid information from the U.S. Patent and Trademark Office. The judge also found that Microsoft did not infringe the patents.

But the U.S. Court of Appeals for the Federal Circuit, in a strong rebuke of the trial judge, ruled Friday that the judge's decision in Microsoft's favor was hasty and clearly erroneous.

The Federal Circuit found that RCT did not, in fact, deceive the Patent Office. The appeals court, finding multiple errors in the earlier legal proceedings, said the case should be reconsidered, and it ordered that the trial judge be removed from the case.

Lawyers for RCT said they were anxious to more forward with their claims.

"We'll move quickly and aggressively to get this case in front of a jury," said RCT attorney Terry McMahon, a partner with McDermott Will & Emery.

Microsoft spokesman David Bowermaster said the company's case against RCT's claims "is still in place and remains strong."

"We continue to maintain that these patents are invalid and are not infringed by technology in Windows or Office," Bowermaster said. "We look forward to going to trial for the first time and telling our story in court."

Microsoft shares recently were down 24 cents, or 0.9%, to $25.48.

-By Brent Kendall, Dow Jones Newswires; 202-862-9222; brent.kendall@ dowjones.com

(Lauren Pollock contributed to this report.)

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