VBoxManage.exe: error: Cannot register the hard disk Virtualbox


I got this error today right after I had moved my virtual machine folder to a different drive.

This is what happened.  I moved the virtual machine folder off my main hard disk to another disk.  I then deleted the listing in Virtualbox and then went to add the machine back.  This is where I get the message.  A very simple step that was missing was for me to  CLOSE Virtualbox and reopen the program.  After that simple mistake I was then able to add my VM and start it.