After many experiments i found that this board's bios REQUIRES that there is a mbr partition marked as ACTIVE. It doesn't try to boot, when there is no ACTIVE parititon on the disk! This may make sense for old mbr, but makes me think that GPT is not supported at all on this motherboard.
Update: i have finally managed to boot my Freebsd on zfs root using a GPT formated disk! The trick was to set the partition in the protective mbr as active. However not all tools will allow you to modify this mbr. The freebsd fdisk did the trick for me.
mgatsev, thanks for coming back to post this solution! I would have never thought of trying such a thing.
I had exactly this problem when setting up Ubuntu Server 10.04 on the D510MO board. Using SystemRescueCd, toggling a partition boot flag in parted, which shows the GPT partitions, didn't help, but toggling the boot flag using fdisk, which only shows the single (MBR?) partition, did the trick.
Intel engineers: hopefully this issue can be fixed in a future BIOS release?