When and why is an std::__non_rtti_object exception generated?

I'm using Visual Studio and performing a valid dynamic cast. RTTI is enabled.

Edit : Updated the code to be more realistic

struct base
{
    virtual base* Clone()
    {
        base* ptr = new base;
        CopyValuesTo( ptr );
        return ptr;
    }
    virtual void CopyValuesTo( base* ptr )
    {
       ...
    }
    virtual ~base()
    {
    }
}

struct derived : public base
{
    virtual base* Clone()
    {
        derived* ptr = new derived;
        CopyValuesTo( ptr );
        return ptr;
    }
    virtual void CopyValuesTo( base* ptr )
    {
       ...
    }
    virtual ~derived()
    {
    }
}  

void Class1::UseNewSpec( base* in_ptr ) //part of a totally unrelated class
{
    derived* ptr = dynamic_cast<derived *>(in_ptr);
    if( !ptr )
       return;
    delete m_ptr;
    m_ptr = ptr->Clone(); //m_ptr is a member of Class1 of type base*
}

//usage : 
Class1 obj;
derived new_spec; 
obj.UseNewSpec( &new_spec );

My debugger says that in_ptr is of the correct type when the exception is thrown. Google seems particularly unhelpful. Any ideas? Cheers.

I ran a test based on your pseudo-code and it works. So if RTTI is truly enabled in your build configuration, then it must be another problem that isn't captured in what you posted.