There are few things that may cause this.
For example if you have Ctrl+B already macroed to something else, this will cause problems.
You can test your CTRL+B and see if it works, by downloading a marco program, also you can play a game with user adjustable controls. For example in World of Warcraft you can program the entire keyboard with hundreds of key bindings/combinations.
So if you have WOW, make a key binding of CTRL+B to do a certain function like ride Mount, and see if your character does it, if it doesn't then, you know there's something acting up.
Also press CTRL+ B (really hard) there may something causing it to not function properlly.