This update on Vista (and server 2008 and Win 7):
Microsoft Security Bulletin MS10-092 - Important: Vulnerability in Task Scheduler Could Allow Elevation of Privilege (2305420)
kills many of the Task Scheduler tasks. See this complaint about KB2305420:
I just spent an hour trying to find out why I was getting a lot of errors in the Task Scheduler. Uninstalling update KB2305420 fixes the problem.