We are building a new corporate image and ran into this error as well. For us, we had to mount the .wim files on something other than the current system volume - we tried to mount to C:\[imagepath]\mount and it gave a whole slew of "objectID in use" errors. They guy training me quickly remembered and had us unmount then re-mount on another volume (in this case an external USB 3.0 drive) and it remounted without error.