You must include the Virtual Panels header files in your modules. The top of your module may look so:
#include <vphead.h> // must be included first, contains
#pragma hdrstop // all necessary standard headers
#include <vpbase.h> // contains basics of Virtual Panels
// Must be included in any case
// These headers are optional. You must include them if you use:
#include <vpbutt.h> // the button system
#include <vpmenu.h> // the menu system
#include <vpled.h> // the LED class
#include <vpboard.h> // the Board class
#include <vpoutbox.h> // the Outbox class
#include <vpinbox.h> // the Inbox or TSInbox class
#include <vpindic.h> // the Indicator class
#include <vpgraph.h> // the Graph class