If vmkfstools fails, the hidden vmware-vdiskmanager tool (available on ESXi but less documented) may sometimes help by attempting to convert or clone the disk.

Few things are as panic-inducing to a system administrator as a virtual machine (VM) that refuses to power on due to a corrupt disk file. Whether caused by a storage array failure, an unclean shutdown, or a failed snapshot consolidation, a corrupt VMDK (Virtual Machine Disk) can bring operations to a halt.