I have the same problem with lvm encrypted with ACER5940g.
it looks like my BIOS freeze and can't pass the relay to grub (only happen with an encrypted lvm).
I found a way to make it works, in BIOS i set my SATA hard disk mode to IDE and now it boot, (it doesn't boot works when SATA mode is AHCI).
tested on ubuntu 10.04.
I have the same problem with lvm encrypted with ACER5940g.
it looks like my BIOS freeze and can't pass the relay to grub (only happen with an encrypted lvm).
I found a way to make it works, in BIOS i set my SATA hard disk mode to IDE and now it boot, (it doesn't boot works when SATA mode is AHCI).
tested on ubuntu 10.04.