invalid argument exception when unlocking machine

Hi,

I keep getting an invalid argument exception when unlocking my machine if I have the scheduler open. The error happens in the following function: -

this.updateHeight=function(){
if(this.nav.scroll){
this.nav.scroll.style.height=this.getScrollableHeight()+"px";
this.scrollHeight=$b.nav.scroll.clientHeight;
}
};

the error is happeining on the following line

this.nav.scroll.style.height=this.getScrollableHeight()+"px";

this.getScrollableHeight()+"px" returns "-24px"