Pure virtual function call

[Audiojack]

Hello. My avast Free doesn't work.

From startup it says "WARNING, your system is UNSECURED" and the taskbar logo has a red ball with a white X on it. Occasionally that changes to a yellow triangle with a ! on it.

If I try "Fix Now", the program just freezes and if I remember correctly crashes at some point.

This computer has a lot of problems on its own but I'm not sure what causes this one.

Now after many hours using the computer, I (being lazy) have been relying on the firewall, but I decided to write here now since I got a rather odd error message pop up from nowhere.

It says this (The first line is the windows header)

Microsoft Visual C++ Runtime Library



Runtime Error!

Program: C:\Program Files\Alwil Software\Avast5\Avast\Svc.exe

R6025
- pure virtual function call



I just pressed "OK" since there were no other buttons, and nothing happened.

So what's the problem?

[Asyn]

Other security related software installed..??
Info about your system..?? (OS, etc..)
Run free Mbam and report your results..! http://www.malwarebytes.org/mbam.php
asyn

[Audiojack]

The OS on this computer is Windows XP Home (32bit)

No other security software except for Sygate Firewall.

Can't be arsed to finish a Mbam scan at the moment, I tried twice and the program froze
(First time because I was using something else and the program was in the background = Instant freeze,
second time because I left it be and the screensaver went on = Freeze)

I'll do it later maybe. This computer is my dads and its rather a problematic one...
But the main thing is I would like to have the antivirus working so I could maybe then start fixing the other ones.. 

[Asyn]

The OS on this computer is Windows XP Home (32bit)

Run a boot time scan with avast..!!
If that works, report back here, if not try this.
1. Run this in safe mode. http://www.avast.com/uninstall-utility
2. Restart.
3. Reinstall the latest version. (5.0.594)
asyn