Just try to do the following:
[root@esx1:/vmfs/volumes/56d97ec1-2b6018d1-5468-b82a72d2f472/1] vmkfstools -t0 DISK-000001.vmdk
Failed to open virtual disk: Input/output error 327689
[root@esx1:/vmfs/volumes/56d97ec1-2b6018d1-5468-b82a72d2f472/1] vmkfstools -i DISK-000001.vmdk DISK-clone.vmdk
Failed to open 'DISK-000001.vmdk': Input/output error (327689).
[root@esx1:/vmfs/volumes/56d97ec1-2b6018d1-5468-b82a72d2f472/1] cat DISK-000001.vmdk
# Disk DescriptorFile
version=1
encoding="UTF-8"
CID=20f463a7
parentCID=89cccd46
isNativeSnapshot="no"
createType="vmfsSparse"
parentFileNameHint="DISK.vmdk"
# Extent description
RW 83886080 VMFSSPARSE "DISK-000001-delta.vmdk"
# The Disk Data Base
#DDB
[root@esx1:/vmfs/volumes/56d97ec1-2b6018d1-5468-b82a72d2f472/1] cat DISK.vmdk
# Disk DescriptorFile
version=1
encoding="UTF-8"
CID=89cccd46
parentCID=ffffffff
isNativeSnapshot="no"
createType="vmfs"
# Extent description
RW 83886080 VMFS "DISK-flat.vmdk"
# The Disk Data Base
#DDB
ddb.adapterType = "lsilogic"
ddb.deletable = "true"
ddb.geometry.cylinders = "5221"
ddb.geometry.heads = "255"
ddb.geometry.sectors = "63"
ddb.longContentID = "c2b1d91676ac94a3c7b2d88e89cccd46"
ddb.toolsVersion = "9537"
ddb.uuid = "60 00 C2 94 e1 10 9b 43-c2 71 bf 48 64 bc 69 97"