Is it a fresh install of NAV 2010 or over-install above NAV 2009? -----over NAV 2009

Do you have any other security programs?-----No

Which is your Operating System?-----XP

Check in the History for any recent errors. If you see any such error for Sonar Protection, check for the error code and module id(You can find it under More Details).

Yogesh

It's doing the same thing on my laptop which suggests that it's a Norton problem.  I turn Sonar on but the NAV software turns it off.