csrutil disable
Restart computer
In the terminal, type
sudo open /Applications/TextEdit.app /System/Library/LaunchDaemons/com.apple.ManagedClient.enroll.plist
change
<key>com.apple.ManagedClient.enroll</key>
<true/>
to
<key>com.apple.ManagedClient.enroll</key>
<false/>
So that the changes take effect
Do you have iCloud logged in on that machine? Log into iCloud and iCloud lock that device. It will generate an unlock code number. I was told the iCloud lock unlock code will overwrite an existing firmware password.