A Mac user with Norton/Symantec software on his machine? Now that's something I would strongly advise against. Most of the admittedly anecdotal evidence is that these packages inhibit the performance of Macs. There are better ways of protecting your machine depending on your need.

And, as a suggested explanation for the quitting phenomenon, I have seen the re-emergence of the problem since upgrading to OS10.2.6 having enjoyed continuous operation under OS10.2.5. Probably just coincidence?