Solution:
DHCP must be enabled on the Perle.
This can be configured in the Server Configuration.
If the bootfile parameter was passed to the Perle then the unit will display the following out the Admin port during the bootup:
INIT: getting boot information file
TFTP: transfer succeeded
INIT: got boot file, xx bytes
bootfile(1): [filename] now taken from host [TFTP IP address]
bootfile(1): [processing information found in bootfile]
Verify that TFTP is running on your server that is running the bootP/DHCP daemon.
Verify that the bootfile parameter is being recieved by the Perle. You can use a network sniffer (such as wireshark) to examine the bootP/DHCP packet.