C/C++ :: Build Error When Trying To Include Another Custom Class?

I have a class like this:

#include <string>
using namespace std;
//-----------------------------------------------
class Prenumeratorius {
private:
string pavarde;
string adresas;
string leidinioKodas;

[code]....

bunch of variables, constructor, setter and getter.And I have this class:

#include <vector>
class Leidinys {
private:
string kodas;
string pavadinimas;
double vienetoKaina;

[code]....

in to my "Leidinys.h" header file, I get a build error, I tried to remove same includes in both files, that didn't worked.