ESXi 4.1
This is a fresh VM that I setup from an ISO of Win2k3. It is not a clone. I've also never snapshot'd it.
I finally figured out how to run vmkfstools -x check [file].vmdk and the result is "error free". Expanding from vmkfstools fails with the same error. I've rebooted the VM and it does not help. If I try to expand while the VM is running, the VM crashes and I get the same error. I've tried expanding with the VM off and get the same error. I've looked through the datastore and it contains no snapshots.