With past experience using Russian equipment, their tollerances in manufacture are sometimes different to those of the likes of Nikon/Canon/Pentax etc. It may be something as simple as the button used to unlock the lens on you camera body may not be being depressed far enough to release the pin. Also with it being a Nikon N2000 which is a Nikon 'clone' body, that is to say, not made by Nikon or under their control may be exaggerating the problem.

As I recall the same body badged 'Olympus' with an OM Mount was made in China.