switch off loading of service. go to control panels, find services applet
(location depends on win version, WNT has it just in control panels, W2K and
WXP has it under computer management console). Look for  not running service
with "automatic" setting for startup and check its properties for service
name and path to see if it is service you are looking for. Set startup
option to "manual" and you will "stop" appearing of this message during
startup.

However, this is not all what you neeed to do. This message means that
system is unable to find file with service driver. This means that this file
is missing, was moved by uncorrect way or your system registry is messed up.
Ususally it is because someone or something deleted object that require
uninstall (or install/unistall procedure crashed in the middle of
operation). This can be also result of virus infection - either virus or
antivirus can delete files they dont like to be in your computer. The basic
action is to look on service properties - there is an image path (ie. name
and location of service driver file) and possibly also some description. If
image path exist, you can look on other files in the same location, as they
are possibly part of the same sw package. This usually tells you what is
this service for or what sw package it belongs to. So you can take any
action like reinstalling of corrupted sw package etc.

I have no idea what is service NAVAPEL for, but NAV can be norton antivirus,
so if you have such thing installed in computer, it is time to check it.