Get "Access Denied" when add or change a crawl schedule

The sharepoint search suddently stop indexing. The content manager link can't access, shows http 403 error, not authorized to view the page, search status is Error. Create a new SSP, change the association to the new SSP, mannualy start the full crawling. It seems everything works fine. However, when try to set up the schedule of full/incremental crawling, "Access Denied" message comes up. Realized a few days ago, to stop the spreaing of AD worm in the organiztion, permission for task folder all have been removed. Reconfigure the permission of the task folders, the scheduled crawling successfully created, also the search service in old SSP back to normal. It seems sharepoint serach service quite relies on windows task.