After formating the disk in freenas with UFS GPT options the bios will not boot next time.
Deleting the partitions makes it bootable again.
Chipset is Nforce 4
Did you have tried to disable drive detection in BIOS? This is not needed because FreeBSD does not use the BIOS to recognize the disks.
The problem is that it seems that your BIOS does not like EFI/GPT partitions. Did you have checked for a BIOS update?
This is a BIOS limitation, unrelated to FreeNAS.
Upgrade your BIOS, change your motherboard or don't use GPT partitions.