Version/build number of BS.Player? Your OS?
"Some movies" sounds rather vague. Any specific type of movies?
When you play those movies, which codecs/filters is BS.Player using?
To find out (with movie loaded!!): rightclick > Options > Filters > Advanced
(Clicking on Source and on the small [+]-signs in front of the filters/codecs shown will reveal further info of (and access to) those filters/codecs.)
Did you install BS.Player using all default settings?
When you installed BS.Player did you allow it to also internally install its preferred codecs/filters? (Internally meaning for use by BS.Player only and not interfering with your system's codecs/filters).
If you didn't you can still do so, using BS.Player's auxiliary application "codecmanager.exe" which you can find inside BS.Player's installation folder.
