I'm afraid this concerns a pre version 1.0 skin.
This way of volume slider only works till BSPlayer's version 0.86 (and no longer for later versions, which - in fact - concerned a total rewriting of BSPlayer). Whereas most pre 1.0 version skins do generally work allright for 1.0(+) versions of BSPlayer (which comes with a plugin just to realize that) this does not cover this particular (indeed for 0.8 skins often used) way of a volume slider.
Maybe one of our skin-creating fellow BSPlayer users could rework this skin (with a substituting volume-slider) to make it 100% compatible with 1.0(+) versions of BSPlayer? C'mon fellows!
