Hi C_virus,
What version of the software are you using? If it is "Norton AntiVirus" then the product is most likely NAV 7.5, which reached End of Life many years ago. Viruses, worms and other threats have become very sophisticated in recent years- the tools used to create them are always evolving. It is possible that the technology in NAV 7.5 could be incapable of remediating a specific infector. As soon as it is safe to do so, upgrade to SAV 10.1 MR9 (the latest release in the SAV line) or to Symantec Endpoint Protection 11. These are fully supported and capable of handling today's threats.
Was the trojan detected by Auto-Protect or by a scheduled/manual scan? Auto-Protect can sometimes detect threat processes that Windows has been "tricked" into protecting. A full system scan in safe mode can usually deal with these.
Finally: know that there are threats which cannot be repaired. If 100% of that exe is malicious, the only safe action for an AV program to take is to delete it.
Please continue to use the forum or contact Symantec Technical Support if you continue to have trouble! Supply as much specific detail as you can about what kind of virus it is, what you are using to fight it, and on what platform.
Thanks and best regards,
Mick