SERVER not defined. Can't change network boot configuration

[walker]

fai version: 2.6.6

when fai almost finished,it output the following lines on screen:

.....
The installation took 493 seconds.
Calling task_chboot
SERVER not defined. Can't change network boot configuration
Calling hook: savelog.LAST
ERRORS found in log files. See /tmp/fai/error.log.
savelog.LAST      OK.
calling task_savelog
Calling task_faiend
......

the line "SERVER not defined. Can't change network boot configuration" 
seems tip that something is wrong, what causes this error? what the 
SERVER do?

Best Regards!
walker