Hello Carlos,
i think there is something else wrong on your site -
are you sure you are looking at the right article?
If the plugin is not active, you should see the invocation code (the "{gpxtrackmap}images/GPX/mapa.gpx{/gpxtrackmap}") in clear text.
If it is active but has some kind of error, there would at least be some sort of
output in the generated page.
Can you look into the php error log and check if there are any errors related to the plugin in there?
cheer, Frank