PHP Code:
<?php $file = get_field('fl_map_id');if(trim($file) != ""){echo '<a class="colorboxiash" href="'http://www.domain.com/wp-content/plugins/leaflet-maps-marker/leaflet-fullscreen.php?marker=' . $file '">' . '<img src="http://www.domain.com/images/map.png" alt="map" />' . Map . '</a>';} ?>
Yep, if you had used PHP tags you'd see that you have an error with the quotes on the href leaving http: hanging, and the rest of the line as a comment. http: itself is invalid in context as it doesn't match a valid constant name, as well as the missing ending } from being commented.
Also a fantastic reason to not put everything on a single line.