Sometimes, only using Unlocker (http://ccollomb.free.fr/unlocker/) or Delete FXP (http://www.jrtwine.com/) you can delete files that, for any reason, have a bad ‘signature’ in the Master File Table (MFT).
Some files could be removed following How to Remove Files with Reserved Names in Windows XP.
See more info: http://forum.avast.com/index.php?topic=15680.0