Not every file type found in GTA is supported by Sollumz.
Ped YFTs (.yft) with articulated skeletons
Skeleton yfts (like mp_f_freemode_01.yft) are supported, as they just contain skeletons. However, some ped yfts also contain additional unknown physics data which is not handled by Sollumz. Here is a list of ped yfts that are not supported.