By default, only processes that are run directly by root are allowed to load kexts. When a user (non-root) process tries to load a kext, an error is logged in system.log similar to:
Request from non-root process 'netbiosd' (euid 222) to load /System/Library/Extensions/smbfs.kext - not allowed.
You can resolve the issue by allowing the specific kext (e.g.: smbfs.kext) to be loaded by non-root processes. This is done by editing the Info.plist file that's included with the kext, usually at /path/to/kext-name.kext/Contents/Info.plist.
sudo nano -w /System/Library/Extensions/smbfs.kext/Contents/Info.plist