Netboot not working

Can you see the netboot server in Startup Disk?

Flush your PRAM to clear out a wonky startup pref?

if the mac is not on the same subnet as the netboot server, N and option won't do much of anything. Does the Mac even try to netboot if you hold down option?

If the Mac IS on the same subnet as the netboot server, the bless command can have some really whacky effects.

Did you place a firmware password on the Mac?

Thanks guys.
Hi Andrew, your made a good guess. Our DP is in different VLan. In the past, I always use bless command to NetBoot and it always worked. So when I had this problem recently, I tried hold down N or Option key, which doesn't see the NetBoot server at all. When I go to preference and start up disk, I can see NetBoot but with a question mark. So I try to verify the NetBoot service on DP. However I experienced another problem:both server app and server admin tool will not connect to my server. It seems not taking my password. I know Apple has a KB article for it but it is not exactly my case.
http://support.apple.com/kb/TS3960
My lion server came with the Mac Mini. It wasn't an upgrade.

Hi guys,
I have placed a second NetBoot server in the same subnet with the client iMacs and they are NetBooting fine. The second NetBoot server is using the same NetBoot image. It tells me there is something different in these new iMacs when they NetBoot.
There are people from Apple forum saying the Lion machine handles DHCP differently but I can't find official document about this. Still no resolution yet.

my netboot stopped working as well.
I tried to follow the procedure of creating a new NBI image using the automator action in the resource kit ,but i still don't have any luck.
I can see the netboot popping up pressing option key at startup, but it just goest through or it come up with a folder icon qith question mark.

PLEASE HELP !
i need to create a new netboot image !!

I am having the same issues. I am using a Mac Mini Server with 8Gigs of RAM. Same Network, same NBI. The Problem seems to have started after the 10.7.4 update.

I'm sure you have tried this but I'll say it anyway. Disable NetBoot and deactivate it all in SA. Hopefully you kept a backup copy of the NBI image. I keep backups of them on our 12 DP's around the world as I've seen NBI sets just stop working. In the worst situations one of the two steps usually works. Another issue I see is if you share PXE and NetBoot on the same VLAN it can cause NetBoot to fail mostly with MBA's. Also it isn't hard just to get IP Helpers put on the VLAN's you want to boot to. It takes about 15 minutes to upload and get the script working for us.