Its likey that it detected the trojan in you system restore where it cannot get to it. Sytem restore points must be deleted (turned off/then back on)
start> control panel>System and maintenance>System>System protection> click "continue">uncheck "automatic Restore points"> click "apply"> then recheck the box and click "apply"
If you are running IE7, then go here to rescan/remove any other infections (set scanner to also scan for "undesirable" programs (i.e., spyware):
Free ESET Online Antivirus Scanner
Also try malwarebytes
note- this software is very limited and is specifically target at polymorphic malware. It is not very effective against other threats. Free version is only for on demand-(real-time scanning is disabled).
This is designed to be used in conjuction with an installed Antivirus- and not as a standalone antimalware program.
http://www.malwarebytes.org/
You can download and run the self diagnostic to check for issues:
ESET SysInspector
To make it easier download and Install NOD32 4.0 Trial, clean your system. You can then remove it and reinstall Norton.
Free Antivirus Download from ESET
NOTE- you must delete ALL system Restore points after the infection is removed. (It will have been backed up as a system check restore) This is the only way to completely remove it.