Linux guest OS won't stay installed between sessions

[Kurtosis]

I'm running Virtual Box OSE 3.1.6 from the repo on Ubuntu 10.04 x64. I've installed Ubuntu Server as a guest, and It was working fine until recently.

Previously I could work in the guest, then logout (of the guest) to the login prompt, then shut down the VM using Machine -> Close -> Power Off Machine. Then I could restart (the guest) and log back in and keep working.

Now however, every time I shut down the guest vm that way (Machine menu -> Close -> Power off machine), the next time I start it, I get the OS installation menu instead of the login prompt.

Not sure what's changed, a recent update maybe (I tend to run Update Manager without first googling to check for regressions). Anyone know what might be the problem?

(I also run Windows XP 32bit as a guest on the same Vbox, but this problem does not occur for Windows.)

[Sasquatch]

Unmount the installer ISO and it's all ok again.

[Kurtosis]

Thanks, I just figured that out and came here to post it. Much appreciated.