There has been an update to the tool to convert a .vmdk to a .vhdk.
Microsoft Virtual Machine Converter 2.0 was released around April of 2014.
Here is the link to the tool: Microsoft Virtual Machine Converter 2.0
The new tool changes the way to convert from using MVDC.exe to using a powershell cmdlet.
I followed this excellent blog to figure this out. What's new on Microsoft Virtual Machine Converter 2.0
Here is a detalied summary of how to do it.
The default install location is:
C:\Program Files\Microsoft Virtual Machine Converter
Using powershell as a local admin you can then load the cmdlet:
Import-Module .\MvmcCmdlet.psd1
After the cmdlet is loaded you can call the following:
ConvertTo-MvmcVirtualHardDisk
This will ask for the .vmdk file path:
Supply values for the following parameters:
SourceLiteralPath: D:\some.vmdk
It will then start the conversion and place the .vhdk in the following path after its converted:
C:\Program Files\Microsoft Virtual Machine Converter
I hope this helps someone else.