First post from a new user here.
I have also been recently playing around with PWM fan control on Raspi Pi 4.
Are you running your script with sudo? I found I got the same message if I ran my script as a user.
In the end I gave up using the GPIO Python module because it only does software PWM, and I found it would use 6% of a RaspiPi4 CPU just running the fan.
There is another library 'wiringpi' which will do hardware PWM, but that library does not currently work with Pi 4. (The author has updated it, but it is not available in Arch or Raspbian mirrors yet), and that library would not work with a Manjaro kernel because it checks for the Hardware and Revision lines in /proc/cpuinfo which are not present in Manjaro.
For an more elegant PWM solution there is a pwm dtoverlay available. Details are in the README in /boot/overlays and refer to this page Using-the-Raspberry-Pi-Hardware-PWM-timers
For my own solution I gave up on the idea of using PWM, because the fans were noisier with PWM than without, due to the windings buzzing at the PWM frequency. Instead I use two small 30mm fans set to turn on at different temperatures.