Hello John
The problem is almost certainly that your button 10 isn't programmed with the CC code for volume (CC7). A strength and a problem with the FCB1010 is that each button can be programmed with a variety of MIDI codes. The easiest way to do this is to use the free utility http://mountainutilities.eu/fcb1010, though you can do it on the unit itself with a lot of button-pressing (see the manual for details).