Then try using the locking key.
How to remove thule roof rack lock.
How to remove thule roof bars step 1.
Once it s inserted fully a quarter turn clockwise should lock in place the mechanism for instance one of the four feet of a car roof rack.
Turn the lock to the unlock position using the regular locking key.
Open the doors on both sides of the vehicle below where the roof bar is mounted.
Remove the master key and try the locking key.
Insert the master key into the cylinder all the way until you hear a click.
Press your finger against the lock cylinder to keep it in place and use your other hand to pull out the master key.
My thule cargo box does not allow me to remove the key when the lock cylinder is in the unlock position a search lead me to a forum thread saying i have to use my key to turn the lock about 15 degrees remove the key the universal change key and then remove the lock cylinder i hope this will help some folks out there.
Twist the knob on the foot counterclockwise to loosen.