From very long time grub-common_1.97~beta3-1~bpo50+1_i386.deb has a bug with Xen VPS. When apt install it and I try update-grub, I got this error:
Searching for GRUB installation directory ... found: /boot/grub
warning: grub-probe can't find drive for /dev/sda1.
grub-probe: error: Cannot find a GRUB drive for /dev/sda1. Check your device.map.
When I use default package from stable release I no have a problems.
I use Debian 5.0.6 (stable) on Xen daemon. Kernel: 2.6.26-2-xen-686