I'm seeing this compile error...
...\sdk\include\mstn\mdlapi\deffiles.h error C2079: 'DefaultFileInfo::fileName' uses undefined struct 'Bentley::BeFileName'
It's cured if I add #include <Bentley\BeFileName.h> to deffiles.h.
I should add that I'm not explicitly #including deffiles.h. The MicroStationAPI header files have lengthy #include lists, and #including a necessary header tends to bring in a lot of unrequired headers as well.