To resolve this issue, you must convert the VMDK disk from a monolithic type to a VMFS type. This can be done by cloning the disk using the vmkfstools -i command.
For example:
# vmkfstools -i /vmfs/volumes/Datastore1/TestVM/TestVM.vmdk /vmfs/volumes/Datastore1/TestVM/TestVMDisk.vmdk
Where TestVMDisk.vmdk is the cloned disk.
The cloned disk can now be added to the virtual machine and the virtual machine should now power on successfully.