sanboot --drive 0x80 (localboot) hangs

[bshogeman]

I have a very strange issue.
On almost any pc iPXE functions correctly. On 15 of them sanboot fails.

The script loads:
sanboot --no-describe --drive 0x80

from a php script on a webserver. 99% of the times this gives no problem at al but at 15 pc's it hangs on the message Booting from SAN.
The strange thing in this is if you press Ctrl-B and typ the command by hand it boots normaly. I also can't find a difference between the machines.
All machines run the same image and an other machine of exactly the same model have no problems at al. The problem isn't isolated to one model.

An other issue is that on some pc's iPXE doesn't return a serial and model. Both variables contain only a space. This is one of the pc's that give the above sanboot error. And again an other pc of the same model doesn't have this problem. On both I can read the model and serial with a wmi query under windows without any problems. Bios update don't solve the problem.

Do you have any suggestions?