Well that's part of it. - antivirus software often causes more problems that it solves on a Mac. There's so little problem with viruses, that most folks get along just fine without ever using that type of software (at least on a Mac)
Your best goal right now would be to remove that antivirus software.
Boot up into safe-boot mode (hold the shift key until you see the rotating gear under the Apple, then you can release the shift key) You will get to a log-in screen, so just enter your admin password.
You'll probably have to go to web site for your antivirus software to find out how to remove it completely.
Do you have an older PPC Mac, or a newer intel Mac? (which Mac do you have?)
You should download and install the current combo updater for your 10.4.11 system, and the type of Mac determines which download you need.