When I first started using the script, I placed it in /usr/local/bin ,
it was then suggested that it would be better off in /etc/dhcp/bin , so
I moved it. This, it appears was a BAD idea, for if you run 'apt-get
update && apt-get upgrade' and isc-dhcp-server gets upgraded,
the /etc/dhcp/bin directory disappears, yes, you read that right, the
script is removed.
How did I find out about this ?
Fairly obviously, I ran 'apt-get update && apt-get upgrade' :-(
Go and read the wiki page ASAP and don't upgrade until you have fixed