Scheduled Full System Scan Stops Running

I have a full system scan scheduled to run through task manager.  I had to stop using the Norton schedule several months ago because it would not start as scheduled after one of the NIS patch updates.  The task manager was a work around for me.  It has been working correctly like this.  Last week the scan started as usual.  When I came back to the computer, the scan was frozen.  I closed it and ran it manually.  This week the scan started as usual.  It was about half way through the scan and I walked away.  When I came back to the computer the scan was no where to be found.  It was not frozen or not running.  Usually when the scan is done, there is a window to indicated the scan is finished with the results.  this did not happen.  In checking the task manager...it indicates that the scan ran.  In checking NIS's scan history...it did not show that the scan ran.  When manually starting the scan, it indicates that the scan last ran last week when I manually started it.  Anyone have any ideas?  Also, I have the idle time scan turned off because I actually run the scheduled scan twice a week.

 

I run NIS 2010 17.7.0.12 with Windows 7 Ultimate 64 bit, 6GB, IE 8, NU 14.5