RH linux 5 server does not boot anymore after kernel update

Hi,

I have some Red Hat 5 Linux servers running kernel version: 2.6.18-164.el5. I need to upgrade at least to version 2.6.18-185.el5 because I want to extend a LVM ext3-partition with more Gbytes. I have downloaded version 1.6.18-255.el5 and did the upgrade on a virtual testserver. On a Xenserver platform it worked but on a Hyper-V server as host, the virtual Linux machine does not boot anymore.

# rpm -U `kernel-files`    (was used as upgrade command)

This seems to work but when i reboot the server it does not startup anymore. It fails on finding VolGroup00.

After putting back the .VHD of the virtual machine, i could get my server back up with the old kernel.

Is this a known issue ? Is there another kernel more recent than 2.6.18-185 that could help ?

Rgds,