On October 22, 2003, at 1730 mountain daylight time, a Learjet 45, N420FX, owned by Bombardier Aerospace Flexjet and operated by Vestar Capital Partners, experienced an uncontrolled spoiler roll event during descent through 13,000 feet mean sea level, while en route to the Denver International Airport (DEN), Denver, Colorado. The flight crew regained control of the airplane, and made an uneventful landing at DEN. The airline transport pilot certificated captain, airline transport pilot certificated first officer, and 2 passengers on board the airplane were not injured. The personal domestic business flight was being conducted on an instrument flight rules flight plan from Teterburo, New Jersey, to DEN under the provisions of Title 14 CFR Part 91. Visual meteorological conditions prevailed at the time of the incident. The company reported that as the crew was descending through 13,000 feet, the captain extended both spoilers as speed brakes to reduce the airplane's speed. The left spoiler came up and the right spoiler barely moved, causing the airplane to roll to the left. The company also reported the pilots saw the amber-colored "Spoiler Fail CAS" light illuminate. The captain retracted the spoilers, rolled the airplane back to a level attitude, and began running the appropriate emergency checklist. The captain continued the descent and landed at DEN uneventfully. The left and right spoiler actuators (part number 6627602001-003) were ground tested at DEN. The tests showed high internal resistance in the actuator coils. The actuators were removed and retained for further examination. Later testing at the manufacturer in Wichita, Kansas, confirmed this finding.