Thanks garlin, I missed the point, it is listed in NTLite as mounted, not that NTLite mounted it.
In that case it's simple, just right-click and Unload on the blue-iconed mounted entry.
It is actually not recommended to manually delete that reg entry as it removes any mounted image references, leaving them mounted in the background.
In the future just use NTLite to unload those, it does it cleanly, and if not possible it will clean the specifically stuck reg entry.
I also did notice in the past that Windows could leave that hanging.