Subtitles are not displayed - MKV file

[nekros]

Hi guys.
I have Haali media splitter for mkv files, and I am using BS player 1.37.826.
So I am playing MKV file that has multiple subtitle options for different languages, but none of them seem to appear. I even downloaded normal srt file but no subtitles are displayed.
When I open BS player options menu, the "Show subtitles S" option is disabled, I can't turn it on.

Just to clarify more, this is not the first mkv file that I played that "refuses" to load any subtitles. Many other mkv files are fine and I do see the subs attached. Others don't show the subs attached, but I can use srt file and then I see it.
But occasionally I can't see subs at all, no matter what I do. Do I have some codec missing or what? Why some of the mkv files that have subs attached don't show them and subtitles option in BS player is disabled?

Thanks.