Hey Giuseppe,
Now the error is fixed. It was unrelated to the hotspots plugin. The error is related to joomla 2.5 and the fact that some core functions have changed...
I've fixed the error on your site and also in the next version of Hotspots. So when you update in April you won't suffer from this again
About your other issue. Go to the categories layout and hover with the mouse over the title of the category - > you will see that the url is something like &cid[]=12. 12 is the real number of the category.
This will change in the next version of Hotspots and you will just have a list with categories in the menu that you create.
If everything is OK now on your site I would appreciate if you could spend few minutes to write a review and to talk about the support here:
extensions.joomla.org/extensions/maps-a-...-locations/maps/9468
Thanks,
Daniel