As soon as I started VirtualBox, it reported one of the storage devices was not accessible. Turned out to be the virtual hard disk for my Ubuntu LTS guest. It was dynamic, 20GB, and contained - to my good fortune - little to no in expendable data. So in the end, I finally removed the vdi from the Virtual Media Manager and removed the vdi from my Library. I had been using Ubuntu for a couple of days, got GNUS working in Emacs, installed git and nothing else. I had the guest edition installed and all the Ubuntu update files that it suggested.
My host is OS X 10.6.4 running on a MBP which has 3GB SDRAM and a 500GB hard drive. Mem. allocated to Ubuntu was 1024.
Has anyone seen this before and did someone manage to make the vdi accessible again?