Scheduled scan fails -- no files found

Using NIS 2010 I set up a scheduled full system scan to run in the early morning hours.  Most mornings I find a message in a box on my screen that says something like "Full system scan failed -- no files found."

 

I note that idle time scans work just fine.  Scheduled scans worked perfectly on this machine (running Windows XP) when I had the previous NIS version, until the NIS 2010 update.

 

Any clues as to why the scheduled scan failes in this manner?