Better debugging

Amazing how a completely fresh copy of windows xp will complain about the slightest code problems ...
My app on windows 7 has a constructor for a graphical pane and the graphical pane has member variables
int w; // screen width
int h; // screen height

now the constructor has an error,

int w = this->GetWidth();
int h = this->GetHeight();

and this is incorrect because they are already declared in the class definition. But the constructor already works in Windows 7!!??!!