ESX 5.1 - cannot power on VM with multiple vmdk files

If you receive the below error message when you power up a VM:

Error Stack:An error was received from the ESX host while powering on VM VM-nameCannot open the disk '/vmfs/volumes/Datastore/VM-name/VM-name.vmdk' or one of the snapshot disks it depends on.The system cannot find the file specified.VMware ESX cannot find the virtual disk '/vmfs/volumes/Datastore/VM-name/VM-name.vmdk'. Verify the path is valid and try again.


Module DevicePowerOn power on failed.
Unable to create virtual SCSI device for scsi0:0, '/vmfs/volumes/datastorename/VirtualMachineHome/VirtualMachineDisk.vmdk'
Failed to open disk scsi0:0: Unsupported and/or invalid disk type 7. Did you forget to import the disk first? 

after upgraded to ESX 5.1, it is probably because ESXi 5.1 turned off the support of multpart vmdk by default.

1. Follow VMWare's notes (2036572) to enable multiextent on ESXi 5.1
2. Covert the multiextent vmdk files to a single vmdk file

In fact, right before ESXi upgrade, it is recommended to backup the VM either using VMWare converter (if you are using thin provision, this is a good chance to shrink the vmdk) or simply export the powered off VM using export to OVF function in vSphere client.