when drag a div with ie, drag function can't work, script thow exception 'error p parameter'. when call setstyle('width', xx), if xx is 'NaN' then exception.
drag: function(event){
....
if (this.options.style) {
this.element.setStyle(this.options.modifiers[z], this.value.now[z] + this.options.unit);} else {
this.element[this.options.modifiers[z]] = this.value.now[z];
}
....
}

this.value.now[z] is NaN, then error.

ok:

if(this.value.now[z])
this.element.setStyle(this.options.modifiers[z], this.value.now[z] + this.options.unit);