xxx.h has
#define EXTERNAL WINAPI
#define RFAR far
.....
.......
yy.h has
#include xxx.h
typedef unsigned short RDM_SESS
.....
.......
typedef void(EXTERNAL *ERRORPROC)(short,RDM_SESS,void RFAR*);
this last line is causing compile errors ( vs 2010) like RFAR illegal use of type void