Although I assume that the command line that you've posted is the result of a copy&paste issue, please try the following:
- open cmd.exe in elevated mode (right click -> "Run as Administrator")
- cd /d "C:\Users\ME\Virtual Machines\Win10"
- "C:\Program Files (x86)\VMware\VMware Workstation\vmware-vdiskmanager.exe" -r Win10-disk1.vmdk -t 2 Win10-pre-allocated-disk1.vmdk
Just to clarify, is the source .vmdk a monolithic virtual disk (a single, large .vmdk file), or is is split into multiple .vmdk files. In case of a split virtual disk, please verify that none of the files is missing.
André