Yes, I tried Unlocker. Problem is, it shows the file is in use only
by Windows Explorer! If I close that, I can't move the file.
As someone pointed out, 'media streaming' being enabled (amongst other
system processes) could be putting a lock on some files. But rather
than going through disabling a bunch of system services or
altering/disabling power management settings, you could try running
msconfig from the command prompt, and disabling everything but a
minimal windows boot, but before allowing your system to reboot, run
unlocker again on the file in question just before that, then reboot
and see if the file is gone. If it is (most likely it will be) then
reenable your system services with msconfig, and reboot once again.