To those who have facing forgot password when you need to uninstall your Symantec AntiVirus, you just need to do the following step then the password will gone: -

1) Goto Regedit.
2) Goto the following directory: - HKEY_Local_Machine\Software\Intel\LANDesk\VirusProtect6\CurrentVersion\AdministratorOnly\Security
3) Looking for "UseVPUninstallPassword", this is a REG_DWORD value.
4) Just change the value from 1 to 0.
5) Close all the application and then goto uninstall again.

The password authentication is gone ..... :)