Honestly I can't (still using XP SP3; maybe a multi-user environment in your case?)
As indicated by BS.Player itself the option "
Open locked media files (files in use)" means: "
If checked BSplayer will try to open files that are in use (still downloading, recording...)".
This is a
BS.Player feature.
However (as mentioned before) the message/error which you get when trying to change a filename of a file which is in use (by any application for that matter) is an
MS-Windows' message.