After installing Norman Virus Control in addition to an antivirus solution from another vendor, the computer freezes completely and I get lots of error messages.
Different antivirus products may "quarrel", as they often want to scan the same files at the same time. This may cause your PC to show some unpredicted and unwanted behaviour
Recommendation: You should uninstall other anti virus software before installing NVC.
If you experience this problem on Windows NT4, 2000 or XP, you may have to start your computer in safe mode to be able to uninstall one of the conflicting antivirus products. To start the computer in safe mode, press F8 during boot, before Windows is loading.