Hi lucaceleghin,
i have the german version of MapPoint and I have the same problem as you have. At MapPoint it self i get results, but in code I don't. But some searchrequests work, for example if I search for "München, Deutschland" it works and also "Munich, Germany" works.
I also guess that this problem is involved with the language. I'm sorry, I can't help you, but i can tell you, you're not the only one