Norton IS 2009 - scheduled full scan aborts

I upgraded from IS 2005 to IS 2009 several days ago.  I scheduled a full scan to begin every day at 2pm.  I had this same schedule for the 2005 product.  I picked 2pm because at that time nobody is ever using the computer.

 

The scan always aborts within the first 30 minutes.  Sometimes after a minute or two, sometimes after 32 minutes.  The time and number of files scanned always varies.  I "chatted" with a Symantec tech who took control of my PC and made some adjustments.  Didn't help.

 

Any suggestions?

 

I'm running Windows XP.

 

Thanks