Looks like you might be publishing to AS3? If so the code you need is different, see below
import net.slideshowpro.slideshowpro.*;
var my_ssp:SlideShowPro;
var paramObj:Object=LoaderInfo(this.root.loaderInfo).parameters;
for (var param in paramObj) {
if (param=="ImagesPath") {
my_ssp.xmlFilePath=paramObj[param];
}
}
HTH :)
Edit: Ooops missed a bit when c&p earlier, sorry half asleep, the import net.slideshowpro line..!