Check setting of "Subtitles disabled" under
rightclick > Options > Preferences > Subtitles >
Also check which codec/filter BSPlayer actually uses for playback under
rightclick > Options > Filters > Advanced (as a filter like ffdshow is also able to play subtitles and thus cause a conflict).
(BSPlayer only supports text-based subtitles natively; read item (9) of my Help2Help-post.)