Longitude spoilers can't arm

That would be because it is fully automatic:

From the Longitude manual:

Ground Spoilers
The ground spoiler system includes all six spoiler panels and is a fully automatic system that does not
require any pilot action.

Ground spoilers deploy automatically when wheel speed is greater than 35 knots and both throttle levers are at approximately idle. The ground spoilers automatically retract below 30 knots, or when the throttles are advanced away from idle. In addition to aiding in slowing the plane, the ground spoilers also reduce lift, increasing the weight on the nose landing gear for optimal steering and braking effectiveness. Ground spoilers extend the spoiler panels 60 degrees.
In the event of a loss of hydraulic power, the ground spoiler hydraulic accumulators will retain enough
charge to power the ground spoilers upon landing or during a rejected takeoff. When the accumulators
are depleted, ground spoilers will no longer function.