The scan failed because of a scan engine problem. Run LiveUpdate to get the latest version

I've just installed antivirus on my MacBook Pro (running Lion 10.7.2).  Cannot get anything to work - constantly getting this error message whenever I try to run any kind of scan:

 

The scan failed because of a scan engine problem.  Run LiveUpdate to get the latest version.

 

Have run LiveUpdate and the software is fully up to date.

 

Any ideas?