Hi Sirrius, The problem was very well described by Ryan. The solution to fix your compilation error is to delete both #include statements. Here is an example of a simple yet correct way to include header files like your are trying to do: File ClassA.h:

#ifndef CLASSA_H
#define CLASSA_H
#include "ClassB.h" // <- Remove this line
#include "ClassA.h" // <- Remove this line
class a
{ ... };
#endif

File ClassB.h:

#ifndef CLASSB_H
#define CLASSB_H
#include "ClassA.h" // Include definition of base class.
class b : public a
{ ... };
#endif

If you want to derive other classes from concAbstFactory then simply include "concAbstFactory.h" in the header files for those new derived classes. Your base classes should not have any knowledge of your derived classes. Hope this helps. :) Eric