This is in the System Event log (Windows Server 2008) ATAPI Event 11 "The driver detected a controller error on \Device\Ide\IdePort2."
It is probably a hardware problem, but I'm not sure how to determine that for sure. The machine still works most of the time, but it locks up at random. Sometimes at boot time, sometimes well after that.
Looking for a solution to a similar problem I came acros this page: http://www.eventid.net/display.asp?eventid=11&eventno=616&source=Disk&phase=1