System Extensions Cannot Be Used Error When installing certain software, usually anything printer related, I receive this error

System extension cannot be used

The system extension "/System/Library/Extensions/Belcarra.
USBLAN_netpart.kext" was installed
improperly and cannot be used.  Please try
reinstalling it, or contact the product's vendor for an
update


This began after I erased some printer folders that I thought I wasn't using anymore.  I'll get about 30 error messages in a row, all with different paths, but all the same message talking about kext files.  I tried fixing permissions with the Mac boot disc, but it didn't seem to help.  I usually just click through all the errors and nothing seems to be affected.  Any ideas how to fix this permanently?
Its possible you deleted some printer folders but left the actual kext files in place.  To delete the kext files that are causing an issue, open terminal and type

sudo rm -rf /System/Library/Extensions/Belcarra.USBLAN_netpart.kext


The system will ask for your password.

Repeat this for any other files the system complains about.  You will then need to reboot.

If something stops working as a result of the above, you may need to re-install the drivers.