It just happened again. Nothing in the log files.
I now have disabled “scanning of created/modified files only”.
Let’s see if that makes a difference.

It looks like it is only happening if I opening a new page, not if I have a page open and just are reading it.

Other applications that where running when it happened:
Seti@home
ZoneAlarm Pro
FireFox
Total Commander
HDTVPCI.EXE (Watching tv on the system through my video/tv-capture card)
Sambar server 6.1