NIS for Mac apparently not set up correctly/not scanning

When I open the Norton Internet Security window, Statistics show last virus scan performed Dec 5, 2011, and Days left in trial as Unknown.  When I click Quick Scan, I get a message "The scan failed because of a scan engine problem.  Run LiveUpdate to get the latest version.  The basic NIS window shows "LiveUpdate occurred, Today at 3:06 AM."  Attempting to run LiveUpdate again, to comply with the error message, nets no new downloads.  Trying to run a Quick Scan again results in the same error message.  I have an order confirmation email from Symantec.  It appears that Live Update is working fine, but scans are not.  What is wrong with my setup?  What do I need to do to fix this?  I am running Lion.