And what does it mean - exactly?
And - although I strongly suspect it's not the drive's fault and also that there isn't one - anyone know how to return drives to their original geometric state after they've been silently corrupted?
It looks like the partition table might be corrupted somehow. You can try to create a new one, but that will remove all the data from the disk. I don't know how or if you do that in Palimpsest (the application you're using), but in gparted, it's easy. Just select the drive and choose "Device > Create new partition table". I'm using a Norwegian translation, so it might not say exactly that, but you'll find it.
From your screenshot, I think that should do it, but it is an assumption. And in any case, make sure you have backups before you try anything.