Hi Jimbo...!
If you have problems in getting Norton to remove a Trojan or Virus, when Windows is running, start the computer in "Safe" mode...
Press the F8 key during boot-up.
When the screen has loaded, locate your CD Rom with the Norton disk in it.
Double click the CD to run Norton scan...

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When running in Safe Mode Windows is not operating, and will not be "using" it's registry, allowing Norton to modify it as required..

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This works much more successfully then trying to get Norton to do the job whilst Windows is running...!
Cheers Jimbo...!
Paul...

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Norton's tip:
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Important: If you are unable to start your Symantec antivirus product or the product reports that it cannot delete a detected file, you may need to stop the risk from running in order to remove it. To do this, run the scan in Safe mode. For instructions, read the document, How to start the computer in Safe Mode. Once you have restarted in Safe mode, run the scan again.
After the files are deleted, restart the computer in Normal mode.
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.