LUKS-partition-failed-to-mount

[Mervyn Zhang <karboninnov@gmail.com>]

Hi all, I'm a debian newbie who are previously using archlinux. I've a
disk with the following layout:

sda1 pri - Windows partition;
sda3 pri - archlinux /boot
sda4 pri - archlinux LUKS partition (with lvm in it, the rest
partitions /, /var, swap and most important /home)
sda5 logic - debian /boot
sda6 logic - debian LUKS partition (with lvm in it, where a base
just-installed system lies)

My two arch partitions remained untouched during the installation of
debian, and no bootloaders was installed since I've already a grub
installed in the MBR.

But when I tried to boot my arch again, the crypt hook reported that

"ERROR:Failed to open encryption mapping: The device /dev/sda4 is not
a LUKS volume and the crypto= parameter was not specified."

So what can I do now to re-access to at least my data? Thank you VERY
MUCH since I forgot to backup them first....