Called by the framework when Excel opens the XLL
[C++]
virtual void OnXllOpen();
This function is called whenever a user loads the add-in, 
            whether using the Excel Tools - Add-ins dialog or directly, 
            using the File - Open menu option. This is a good time to do any initialization that needs to precede any use of your 
            add-in functions, so long as the initialization cannot fail. The default implementation of this function does nothing.
Header: xllplus.h
CXllApp Class 
					  | CXllApp Methods			 
					  | CXllApp::OnXllOpenEx()			 
					  | CXllApp::OnXllClose()