PXE menu not honoring master passwd

[Bob <bobnlinux@gmail.com>]

Hello list,

I have configured a tftp server on debin jessie and the PXE boot is running well. The following is working to protect a single label

label Install debian jessie
menu label install debin jessie
menu passwd mypassword
...
...
..

Now I like to secure all the labels with single password. 
when I put master passwd to protect all the labels as below , it is not working


....

default vesamenu.c32
prompt 0
timeout 0

menu title PXE boot
menu master passwd mypassword

label .1....
..
....
label .2.....
...
.....

I have already done some research and found "master passwd" is the syntax to protect all the labels.
Could any one point out the missing part here ?

Thanks for your time.