Why multiple inheritance fails

I have following multiple inheritance logic

        A
     / B C
     \ /
       D
here A B and C are pure abstract base classe and D is derived publicly(no
virtual inheritance ) from B and C and implements all pure virtual methods
of parent classes

I am able to call A::Method from

D* pD = new D;
B* b = pD;
C*c = pD;
c->method_of_A();
b->method_of_A();

but NOW !! in following scenerio

           A
         / / \ \
     / \ \
   B B2 C
     \ / /
      \ / /
        \ /
           \ /
             D

here A, B, B2 AND C are pure virtual classes and D is derived publicly(no
virtual inheritance ) from B, B2 and C

now here I am not able to call A::Method from

D* pD = new D;
B* b = pD;

b->method_of_A();//not compiling ambiguous call

following is example

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/// why multiple inheritance of interfaces (pure ABC) work when inheritance
hiearchy is liniear but fail when it involve loop
///
class Animal

{
    public:
        virtual void walk()=0;
};

class Cat : public Animal
{
public:
    virtual void Meo()=0;
};

class PussyCat : public Animal
{
public:
        virtual void PMeo()=0;
};

class persianCat: public PussyCat,public Cat
{
public:
    virtual void PerMeo()=0;
};

class Dog : public Animal
{
public:
    virtual void bark()=0;
};

class CatDog : public Dog,public persianCat
{
public:
    void walk()
    {
        printf("Animal Walk");
    }

void Meo()
{
    printf("meo");
}

void PMeo()
{
    printf("Pmeo");
}

void PerMeo()
{
    printf("Permeo");
}

void bark()
{
    printf("bhao bhao");
}

static CatDog* CreateInstance();
private :
    CatDog(){};
};

CatDog* CatDog::CreateInstance()
{
    return new CatDog;
}

int _tmain(int argc, _TCHAR* argv[])

{
persianCat* pPerCat = CatDog::CreateInstance();
CatDog* pCatDog = CatDog::CreateInstance();

pCatDog->walk();//Don't get error
pPerCat->walk(); //Get Error here why I don't know

delete pPerCat;
delete pCatDog;

return 0;

}