I used the update manager to upgrade Xubuntu from 8.10 to 9.04. Other than a samba issue, everything was smooth.
I restarted the machine, and now it won't boot. It's stuck on:

Boot from (hd0,0) ext3     <GUID here>
Starting up ...
It may be related to the fact that the installation is on a VMWare virtual machine - but I'm not sure.

Any idea what went wrong and how to fix it?