BSplayer screencapping

Hello, I've got a question reguarding screencapping. I play all my movies [and the like] in BSplayer (they won't play in anythign else, so I can't take screencaps in any other program) and cannot figure out how to take screencaps. When I try the "print screen" button, where the image should be only shows up as a blank space, and this is the only technique I know of to take screencaps.
Please and thank you!

EDIT:// Thank you so much! Thanks to everyone's help, I can now take screencaptures! Again, thank you very much!