If you receive a message box like the one shown in the image below when attempting to mount a drive on macOS, it may be due to the presence of multiple virtual devices on your Mac, such as VMWare, Virtual Box, Intel HAXM, TunTap, and others.
This is a known issue with macOS, and it occurs because FUSE (Filesystem in Userspace) needs to register a virtual device for exchanging messages between the kernel and the actual file system implementation running in user space. However, the number of available device slots is limited by macOS. If other software on your system is using up all the available device slots, FUSE will not be able to register its virtual device.
By default, a brand new installation of macOS 10.12 has six free device slots. However, VMware and VirtualBox require multiple slots each, TunTap (VPN) requires two slots, and Intel HAXM requires at least one slot. You can use the command “kextstat | grep -v apple” to list the current virtual devices on your system.
One possible solution is to unload the virtual device using the “kextunload” command. However, keep in mind that this is only a temporary solution since the virtual device will be allocated again on the next reboot. Consider uninstalling some of the applications that use virtual devices to free up device slots. Note that you do not need to uninstall the FUSE filesystem kernel extension to fix this issue.