I'm running Bit Defender Antivirus 2009 on an ACER Aspire 5002 (I know, never again), with Windows XP, Version 5.1, Build 2600 and Service Pack 3.
The Status says that I haven't run a Quick System Scan for 21 days and when I click on the FIX button, the scan starts. Then approximately 1 minute later, the laptop shuts down................. 
Anyone else having this problem? Thanks!