Try this (free).....
http://ccollomb.free.fr/unlocker/
Once unlocked (if it was) deletion should not subsequently be a problem.
NB: There is also a 'file delete' facility for files jammed in the Windows memory under Config... > Misc Tools, in
HijackThis
(see bottom image on this link; third button down under 'System Tools':
Delete a file on reboot...)