SCRIPT438: Object doesn't support this property or method

I have been using the Opener property for single input objects and have not had a problem. It is when I apply it to multiple select objects that cause a problem. Here is an example of the code I am using.

function UpdateSelected(){

var catsel=document.theForm2.category

var catname=document.theForm2.catname

opener.document.theForm.btnslctd.length = 0

opener.document.theForm.catslctdh.length = 0

var j=Number(0)

for (i=0i