Maybe you could reveal some information.
E.g. version/build of BS.Player (Free/Pro).
Your PC's OS; if Vista/7 is UAC active?
BS.Player installed with all default settings or ...?
Any codec
packs installed?
(I've always advised against installing codec-packs!) Did you allow BS.Player to download/install
(internally=for use by BS.Player only) its preferred filters/codecs upon installation?
Type of video when problem is there?
Filters used for problematic videos?
For that last question:
With a file loaded (rightclick >) Options > Filters > Advanced
Note: click on the small [+]-signs in front of the codecs/filters to otain further info and access.