Norton Internet Security cannot be reset to defaults

I recently began to have trouble with Norton Internet Security on my Windows XP machine.  The Windows XP instance is fully up to date.

 

The real time protection settings in NIS are set to their non-default values (generally, OFF).  I select the options of returning settings to defaults, but when I check settings again, they are not set to defaults.

 

This is a fairly recent problem on a machine that has been running NIS for 10 months.

 

I recently uninstalled, then re-installed NIS.  That solved the problem until the next time I rebooted- problem is now back.