There’s no POI limit in the plugin, but your blog can run out of memory. It doesn’t seem likely that’s the problem – 67 isn’t many posts and if you ran out of memory you would probably just see a spinner instead of the map, not an error. Memory issues are covered here: http://mappresspro.com/mapress-faq
Try deactivating all of your other plugins and switching to a standard theme for a moment, to see if it’s something else.
in fact 67 then seemed to be very few out of bounds (if there was), I do not know how, but de-serializing the data in the database, the user had inserted some that were then compiled without the address field (NULL). Thank you very much anyway. ciao