When the NIS 2009 upgrade from 16.0.0.125 to 16.1.0.33 occurred, it did not adjust the path of scheduled scans in the Task Scheduler. These paths have the version in them; therefore, after a version update the Task Scheduler can no longer find its target activation. The users have to delete scheduled scans from the Task Scheduler and build new ones.
Also when scheduling a scan in Vista, the scan setup should automatically invoke "Run with highest privileges"...just my opinion.