Your vmsd file is invalid. That why the snapshotmanager can not evaluate the scenery.
Snapshot-vmdks are named "name-00000*.vmdk - 6 digits number.
Vmdk-slices use only 4 digits - the first is either s(parse) or f(lat) : name-s00*.vmdk or name-f00*.vmdk
If in doubt look the vmdks up in the vmware.log - the types are mentioned when they are loaded
Ulli