JS null error with tree view control

Hi,

We have the FCK editor control on an ASPX page along with a tree view control from ComponentArt. When the editor is visible and we select a node in the tree view control, the following JS error is raised within the FCK code:

'null' is null or not an object

This occurs in the following function:

function Window_OnBeforeUnload()
{
FCKToolbarSet.Collapse();
var e;
for (var j=0;j<aCleanupDocs.length;j++)
{
var d=aCleanupDocs[j];
var i=0;
while (e=d.getElementsByTagName("DIV").item(i++))
...

The last line of code causes the problem because the variable d is null.

Any ideas how we can fix this?

Thanks,

Jason