Gah an antispyware program killed my windows

I have no idea why but I have lost more windows installs to antivirus/antispyware programs than I have to viruses and spyware.

So far the count is
Norton - 1
Symantec - 2
Spybot - 1
Viruses - 0

And I didn't have my old xp disks so I had a forced upgrade to vista