Javascript error


I'm using javascripts to handle onchange events of listboxes and it works fine for me. But... On some systems it creates javascript errors like "error: 'document.all.wtSelectGroup' is null or not an object"
It will work after clicking the error away but It's not pretty having these errors everytime there's an onchange event.

I'm using the folowing script:

"<script language='JScript'>
function refreshSelect(){;


Does anybody have a solution for this?
OK.... Nevermind this. I found out the problem. It was because my list boxes were inside if components so they were not always available and this would create the error. And on some systems this error would come as a popup and on some computers only in the status window.