[Yaffs] Difference between Yaffs-single and Yaffs-multi

Hi folks,
as subject can anyone explain me the difference between Yaffs-single and
Yaffs-multi?
It seems that there is a problem with last version of yaffs and you can compile
only Yaffs-multi source because if you try to compile yaffs-single you have a
lot of error.

Thanks
Luca