some other host may keep trying to infect you: and your protection keeps disinfecting the file that the other host may have been copying there. Please see if you enabled Blocking and set an interval to block infecting hosts (OAS scanner module - Properties - General Settings - Blocking tab), if the folder where your protection indicates the infection is shared.
Also, your machine may be infected not only from the outside, but the inside. There are many types of malware, including viruses, worms and trojans, and many subtypes are password stealers, keystroke loggers and downloaders. What you may have is an undetected downloader that is re-infecting your system, in which case you would have to assume that your machine is still infected. Also consider that an infection may be spreading through a thumb drive or a file share. (Thumb drives are a common infection vector, and is becoming more common). While I'm not sure what your environment is, our business environment handles such "chronically" infected machines with an OS rebuild (don't use a settings wizard, migrate documents, and maybe favorites, manually).