Similar to
this (click here)?
What version of BS.Player are you using?
Can you remember any special actions/occurrances prior to when this issue started?
Perhaps played a bit with Key definitions?
Try if "undefining" of any key selected for "Chapter viewer" solves your problem:
rightclick > Options > Preferences > Key definitions & WinLIRC
Then select "Chapter viewer" and check in the right hand column if the boxes still show "???" like the image below.
If not place cursor over (or in) the box in question and depress [Backspace]-key 2x.
Do so for both Windowed mode and Full screen mode and click [Close].
Any changes in behaviour when playing a new movie?