Sonar component stopped working

Since yesterday the Symantec Endpoint Protection on my window XP repeatedly give an error message "SONAR Component has encountered a problem and needs to close.  We are sorry for the inconvenience".  Then the Proactive Threat Protection becomes disabled, wrongly stating that "Protection definitions are too old for Proactive Threat Protection. Click Fix to update prtection definitions." Of course the definitions are updated, but the Proactive Threat Protection simply remains disabled.

I found an old thread (https://www-secure.symantec.com/connect/forums/son...) and realized this is a time-worn issue. Apparently it's come back again. Would anyone please come to my rescue? Thank you so much!