I have a headless Ubuntu Server 11.04 box. If I use:

sudo shutdown -P now

It works every time. However, if I instead want to simply restart the machine:

sudo shutdown -r now

It fails to do so. Here's a screenshot of what I get when I attempt to shutdown with restart (couldn't figure out which log to get this from). It simply spits this out on the screen and then doesn't progress any further. I have to hold the power button in to turn the machine off after this:

(link to full-size image)

Can anyone surmise what might be the problem here? Or perhaps provide some guidance as to how I might diagnose this?