with Norton cnavextbho , winxp closes IE8

W/ winxp sp3, data execution prevention closes win IE8 on startup. Ran NS full scan, Maleware, & Win malicious software removal w/ no threats found. IE8 runs in safemode or w/ add on's off. W/ "cnavextbho  class"  add on  disabled, IE8 runs. It's a "browser helper object" & part of N antivirus.  What does cnavextbho do?  Can I run without it?  Better solution?  Initially w/ cnav...disabled, Live Update gave 3048,3 error. After restart, gone. Foxfire ok w/ cnav.. enabled.

Michael