Sorry for waking this thread (it's THE google hit)...
Just to clarify this for posterity,
If you add a static reservation outside of the DHCP server's subnet,
as in, if you typo one octet, or decide to do another subnet just because,
your DHCP server will be offline after reboot. No errors, just silently not serving.
From command line, you'll see the error though:
admin@gw1# commit [ service dhcp-server ] Static DHCP lease IP '192.169.1.79' under mapping 'CustomerLaptop' under shared network name 'LAN' is outside of the DHCP lease network '192.168.1.0/24'. DHCP server configuration commit aborted due to error(s). [edit]