Symptoms:
When using QueryChangedDiskAreas with changeId set to "*" to gather information about snapshots, you see a FileFault error if changed block tracking (CBT) is enabled on the virtual machine with existing snapshots:
Cannot compute changes for disk /vmfs/volumes/4b42258a-3c6b0036-85af-0015c5f0ebb5/SUSE 11 64-bit_1/SUSE 11 64-bit_1-000001.vmdk: Unknown change epoch.
[2011-01-26 14:44:00.544 F5610B90 info 'Vmomi'] Throw vim.fault.FileFault.