Emma
I have found Event ID: 3036 errors hard to resolve. Windows Search is difficult to configure.
This note might be worth following up, especial with heap corruption in mind:
Errors details: "The URL was already processed during this update. If you received this message while processing alerts then the alerts are redundant or else Modify should be used instead of Add. (HRESULT : 0x80040d0d) (0x80040d0d)" - One user had his Windows 7 system freezing at startup and this event being the last one recorded in the log. After several other troubleshooting attempts, he replaced the RAM on that system and the problem was fixed.
Source: http://www.eventid.net/display-eventid-3036-source-Search-eventno-8822-phase-1.htm
I would check your RAM.
http://www.sevenforums.com/tutorials/715-memory-diagnostics-tool.html