Something to try:
Open Notepad
Choose File -> Open...
Open C:\autoexec.bat
If you see any lines referring to the Symantec file, add the word "REM " (no quotes) at the front of the line. That 'disables' that particular line from running.
If you make changes, save them.
Also open/check/REM any lines that refer to symantec in the file: C:\config.sys
Lastly, check C:\Windows\System.ini for a line referring to symevnt.386. If you find it, delete it.
In most issues I've dealt with Norton and Win98, the offending line has been found in the three files mentioned above.
If you didnt find the "symevnt.386" reference in the registry, then you probably dont want to mess around in there. (Your efforts might be fruitless.)
Lastly, you might want to just re-install NAV, and then uninstall it (restarting when it prompts you to.)
- rp