From MSDN

Compiler Error C2352
'class::function' : illegal call of non-static member function

The specified nonstatic member function was called in a static member function.

The following is an example of this error:

class X
{
public:
static void func1();
void func2();
static void func3()
{
func1(); // OK, calls static func1
func2(); // error, calls nonstatic func2
}
};

==========================================
Your myCallbackFunction() uses non-static members, so we have to try the this pointer approach.

typedef (myclass::*PFN)();

PFN pfn=&myclass::myCallbackFunction;
........

API_function((DWORD_PTR)this->*pfn);