SRTSP Event ID 4 - Error loading virus definitions.

I'm using Norton Antivirus on Windowx XP, and for the past few months my system log file shows this error:

 

SRTSP Event ID 4 - Error loading virus definitions.

 

I've searched the web, and the only thing I've found were solutions to fix the problem if I have corporate Symantec antivirus.  Those directions don't work for Norton.  The files they mention don't exist on my computer. 

 

I've tried removing Norton using Norton Removal Tool and reinstalling.  I still got the error.  So then I removed it again and painstakingly removed every reference to Norton or symantec in the registry, removed every file or folder that norton removal tool left behind, and then reinstalled.

 

I STILL get that error in my log file every day.  Sometimes more than once a day.  I've had Norton on this computer for about 2 years, and had no problems before this.  It really worries me, because if it can't load the definitions, then it's not really protecting me.

 

I installed an removed a couple of other antivirus programs in between when I deleted norton and reinstalled it, just to make sure I didn't have a virus.  I don't.

 

Does anyone have any idea what to try next?  Thanks.

 

System:

Win XP 32 bit

Q9450 Intel processor

4GB RAM