Hi there.
I've had the same problem in a long time. Tried every solution in every forum (i think), with no results...
Then after reinstalling the program (maybe the 100th time i did it) i noticed that an .exe program, a part from the original BSPlayer was trying to get full Permissions before i could get to see my movie... I said no (just to see whats what), and no more error message.
Figured that, or maybe not, it might have been an attempt from BS team to create an .exe solution for Win Vista and Seven that is buggy,
Anyway, after saying no, the same .exe popped UP every single time i went to see a movie, play a music etc...
To stop that i tried something like this:
http://img607.imageshack.us/img607/3189/referencex.jpg
Removed the .exe from the folder, backed it up...no more pop up or error message :D.
Hope it works for you too.
PS: I tried to put the image inside the post, but it was to big >.<