Hello miguelramalho,
this is mostly caused because no "slots" are available to load the kext.
Do a "kextstat" via Terminal and check to see if you have a lot of "other" kexts loaded (VMWare, VirtualBox, OPenVPN, etc.)
Then unload the kexts which you don't need, for instance for VirtualBox:
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sudo kextunload -b "org.virtualbox.kext.VBoxDrv"
sudo kextunload -b "org.virtualbox.kext.VBoxUSB"
sudo kextunload -b "org.virtualbox.kext.VBoxNetFlt"
sudo kextunload -b "org.virtualbox.kext.VBoxNetAdp"
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Best,
Yasmin